Sorcerer homebrew ability - balanced? If not - how to make it so?

[Forechosen]

Hi everyone,

So my sister wanted to play a Pyromancer type Sorcerer character - and she wanted a cool ability to reflect that, sort of like a 'heating up' mechanic. My DM and I had a (quick!) think, and came up with the following:

''Each time you deal damage with a fire spell, add 1d4 to the damage roll. This die size increases for each successive spell that hits an enemy, to a maximum die size of d20. When the die reaches d20, you take half the value of the dice rolled as damage to yourself. This damage cannot be prevented. The die will automatically reset itself back to d4 if you deal no fire damage during your turn.''

Ok. So the idea is, your (fire) spells grow progressively more powerful - if they hit - but at 'max power' they will damage you, to counterbalance it. Now firstly, I understand the ability is terribly written - we wrote it on the fly, and I'm sure there must be a more concise and accurate way of writing that out. I mean, for example, 'each time you deal damage' was not meant to include single spells that do damage multiple times, such as Scorching Ray - but how do you write that out clearly?

But more importantly, the wording aside, is it balanced? Frankly, we found it difficult to judge. A Draconic Sorcerer for example, gets to add their Charisma modifier to their (insert element here) spells - which would almost always be +4 or +5. With our ability, the damage would only be (on average) +5 after three consecutive spell hits (when the die is a d10) - which seemed fairly balanced to us, as three consecutive hits is by no means guaranteed. Sure, the ceiling is a lot higher, but you've got to be lucky.

Anyway, what do you guys think? Overall, we like the idea of 'growing power', having an element of luck, and a risk/reward type system, as it all seems very 'Pyromancy' - but we'd genuinely love to know how balanced this sounds from any more experienced players. And, if it's sounding completely absurd, what might we do to change it, whilst sticking to the rough concept?

Thanks very much for reading!

[MrStabby]

Interesting.

My first thought was that if it were to replace the dragon sorcerers level 6 ability it would be weak. As in actually very weak. It has a number of disadvantages:

1) almost always lower damage
2) the earlier rounds of a fight are more important and you want to front load your damage. An epic fireball is kind of crappy if it only hits two enemies as the other 6 died before it lands
3) it ties you in to dealing damage spells. If the fight calls for a control spell then you lose all your benefits
4) if you want to use your concentration that fight then it is at least one turn further into the fight till you break even

On the other hand... the sorcerer can pull it off better than any other class. There are some relative upsides:

1) quicken and (depending on how you rule it) twin metamagic could ramp you up multiple die sizes in one turn. This makes things a lot better
2) it is a die so critical hits on attack roll spells just got a little bit bigger.

All in all I think it is a weak feature as it impacts too late, it pushes you to cast spells suboptimally and it offers no flexability.

I think that it would still be conservative to start the die size one step higher (d6) or to not increment the size but instead add d4s. I would also suggest that when you dont deal damage by casting a fire damage spell the power steps down one increment rather than resetting so there is less of a punishment for casting something else.

[Forechosen]

Oh wow, thank you for the feedback! That wasn't what I was expecting. Honestly, I'm nervous whenever I try and homebrew extra damage into anywhere. I'm really glad this doesn't appear overpowered or anything.

We did think about upping the starting die at certain level increments, such as d6 at level 10, and d8 at level 15 (or whatever) - but really, those levels are so far away now, we hadn't put much thought into it.

I do really like the idea of the die stepping down an increment, rather than completely resetting. As you say, it feels a little more fair, and it's completely within the thematic too (cooling off, so to speak).

We did consider metamagic and how it would step up the die, but really we thought that was a nice bonus, and a way to manipulate the mechanic to some extent, exactly like you said.

As far as being tied into damage spells, well, honestly that's what she (my sister) wanted - her character is really an absolutely classic 'blaster' sorcerer, just madly throwing out destructive spells. It's not the deepest build but she finds it fun!

[MrStabby]

You could have a temperature dial type effect.

Heat spells push it up, cold push it down. So if it has a positive value it empowers fire spells, if negative cold spells. This would enable the sorcerer to have something to do vs fire resitstant/immune enemies.

Same theme... ish. Same focus on blasting. More flexability?

[Forechosen]

You could have a temperature dial type effect.

Heat spells push it up, cold push it down. So if it has a positive value it empowers fire spells, if negative cold spells. This would enable the sorcerer to have something to do vs fire resitstant/immune enemies.

Same theme... ish. Same focus on blasting. More flexability?

Ahhh see I really like that idea, but I genuinely don't think my sister would go for it - her character is very fire focused. I know for a fact she'll be taking the Elemental Adept feat as soon as possible, to deal with resistance, though admittedly immune would still cause an issue. Hopefully there wont be too many of those enemies.

That being said, I will mention it to her! But that's just my hunch.

Still, let's say the die starts at d6 instead of d4, and the die jumps down in increments instead of resetting - that isn't that much different now than the Draconic Bloodline ability, is it?

They're both tied to a specific element. This ability has an average of 3 damage vs 5 (or 4) for the Draconics- but only on the first spell attack. After that, the disparity closes up pretty quickly, especially if you're using metamagic. Plus, with the die going down in increments, assuming you hit more often than you miss, your die is going to constantly increase - though it could potentially be a slow process, metamagic (or a little luck, or both) ought to help. I mean honestly, with metamagic, you could quite feasibly rank up the die pretty quickly.

I don't know, this doesn't seem too weak now does it? What I'm thinking is that a d20 die obviously has an average of double what the Draconic Sorcerer gives you - double sounds like a lot, it shouldn't be too easy or consistent to get to d20, should it?

[Amnestic]

I wouldn't tie it to dealing fire damage, just casting a fire-damage spells.

It cuts out weird cases like scorching ray's multiple hits and it means that if they miss when casting Firebolt they still keep the dice stacking. The theme/narrative is that casting fire spells is heating the caster up, so actually hitting with the spell to make the dice go up doesn't really make sense to me.

This could pose issues with them spamming firebolt before combat but you can handwave that away by just saying "it doesn't work unless the THRILL OF COMBAT is upon you" or something, so it only works when initiative has been rolled, and even then you only need to worry about that if your player is one to abuse it and, realistically, most aren't.

The flipside is that combats simply might not last that long. I don't know how many rounds your combats are usually lasting for but in my experience three is commonly called out as the average length, and they'd need double that to reach the 'overheat' dice size from d4 to d20.

I love the idea+concept of heating up as a sorcerer subclass mechanic though and might steal some ideas here.

[Forechosen]

I wouldn't tie it to dealing fire damage, just casting a fire-damage spells.

It cuts out weird cases like scorching ray's multiple hits and it means that if they miss when casting Firebolt they still keep the dice stacking. The theme/narrative is that casting fire spells is heating the caster up, so actually hitting with the spell to make the dice go up doesn't really make sense to me.

This could pose issues with them spamming firebolt before combat but you can handwave that away by just saying "it doesn't work unless the THRILL OF COMBAT is upon you" or something, so it only works when initiative has been rolled, and even then you only need to worry about that if your player is one to abuse it and, realistically, most aren't.

The flipside is that combats simply might not last that long. I don't know how many rounds your combats are usually lasting for but in my experience three is commonly called out as the average length, and they'd need double that to reach the 'overheat' dice size from d4 to d20.

I love the idea+concept of heating up as a sorcerer subclass mechanic though and might steal some ideas here.

Oh that's a good shout about having it tied to the spellcasting, rather than the damage. So I suppose going with that thread, the die would go down when ''you haven't cast a spell that deals fire damage this round''. That makes sense!

edit: actually, wait, on further thinking - this completely removes the element of luck, if just casting the spell increases the die, that means as long as you keep casting fire spells, your die is going to increase. I see what you mean about the 'heating up' not fitting thematically with the spells actually hitting or not - but surely the die increasing being 'automatic', is veering on too powerful isn't it? Essentially it would guarantee +d20 damage to your fire spells after 5 (or less with metamagic) turns of combat.

And yeah regarding spamming firebolt pre-combat, in our campaign that absolutely wouldn't be an issue, my sister isn't a meta-gamer like that at all. But still, might be worth putting in the description somewhere just to be complete.

Combat in our games honestly seems to go on for a little while, most definitely longer than three rounds. It's hard to put a number on it, but I'd say it might be closer to five rounds 'on average' - if not even longer. For some reason we just don't have short combat!

[MrStabby]

If you want more "luck" one option is to determine your background "temperature" when you roll initiative.

Start on 0, start on d4, start on d6, start on d8 as determined by a d4? Or even incremented above that if you want.

Honestly, if your sorcerer is just blasting away they are unlikely to overshadow other players even with a pretty generous feature.

[Forechosen]

If you want more "luck" one option is to determine your background "temperature" when you roll initiative.

Start on 0, start on d4, start on d6, start on d8 as determined by a d4? Or even incremented above that if you want.

Honestly, if your sorcerer is just blasting away they are unlikely to overshadow other players even with a pretty generous feature.

Ohhh that's an interesting idea! I do like that.

And aye, that is quite possibly very true! Although none of us really make 'meta' builds at all, we're much more RP focused. Having said that, our party is very damage heavy -

Phantom Rogue
Swashbuckler Rogue
Devotion Paladin
'Pyromancer' Sorcerer
Lycan Bloodhunter

But you're right, I mean, everybody is doing very respectable damage - I doubt my sister is going to outshine anybody. I suppose we wanted it balanced for the sake of.. well, fair play. Rather than how it would work in our specific campaign.

[micahaphone]

Have you looked at KibbleTasty's phoenix Soul homebrew/update of UA? It's got a short rest rest recharge "power up" mode that has a cool charge system where you "cool down" if you're not actively feeding the flame


https://www.gmbinder.com/share/-MC_NZv_di0q9kSfvPpF


on reddit's "dndnext" just this morning they were discussing what if sorcerers had a "rage" type mechanic, maybe as a short rest mechanic

[Amnestic]

edit: actually, wait, on further thinking - this completely removes the element of luck, if just casting the spell increases the die, that means as long as you keep casting fire spells, your die is going to increase. I see what you mean about the 'heating up' not fitting thematically with the spells actually hitting or not - but surely the die increasing being 'automatic', is veering on too powerful isn't it? Essentially it would guarantee +d20 damage to your fire spells after 5 (or less with metamagic) turns of combat.


If you're solely comparing this feature vs. draconic then I understand the concern re: power level, however there's a few things I'd consider - the other features the subclasses brings to the table (eg. free mage armour+1HP/level for draconic), the 'blowback' of this feature at max diceroll, and if it even matters that it's more powerful at all. Firstly in that is draconic the height of damage-based sorcerer subclasses, and should you go beyond that? I think it's fair to say you can.

If you were playing with a draconic sorcerer as well as the pyromancer I'd be more wary but you should be looking not at Draconic vs. Pyromancer but instead Pyromancer vs. the rest of your party. This isn't an officially printed subclass, it's a homebrew thing for your table, so tweak it for your table and beyond that...I don't think it matters. As long as pyromancer isn't overshadowing smitenova or the sneak attack duo all the time for damage it should be fine.

Another idea you may want to consider would be a sliding scale of 'heating up' depending on spell level. Example: Cantrips maybe only increase the die size by 0.5 (so you need two cantrips to go up a size, slowing that down a bit), maybe 1st-3rd level spells increase it by 1 die, 4-5th by 2 dice, 6-7th by 3, etc.? More powerful fire spells making you heat up more.

That could mean at high levels they're overheating very regularly if they're blowing lots of high level spell slots on fire spells, upcast or otherwise - and I think that's cool.

[Avonar]

How about this?

"Once on each of your turns when you deal fire damage with a spell, you gain a Flame Charge (insert better phrasing).

Whenever you deal fire damage with a spell, you may expend any number of flame charges. If you do, you deal an additional X d6 fire damage. You also take fire damage equal to half of the additional damage rolled. This damage ignores resistances and immunities. If you spend any flame charges to deal additional damage, you do not gain any Flame Charges."

You could also then increase the size of the flame charge dice at later levels.

Admittedly I just made this up now and am very unsure how balanced it might be. You could also have it so you gain charges equal to the level of the spell that dealt the fire damage. That way you can't just ramp up with cantrips, but dropping big fire spells comes with more benefits?

[Nagog]

I like this idea, but I'd also consider balancing it to having a total number of steps to maximum equal to your Proficiency bonus. So at 5th level, it unlocks the capacity for 1d8 to be your cap, before that it charges up over two rounds but caps at 1d6. With that adjustment, I'd hold on the self-damage until at least the d10 mark, as taking half damage every other round at levels 1-4 can be rough.

That said, combining it with Genie Warlock and the capacity to add Fire damage to an attack 1/round could make for a really fun Bladelock build with this ability. I could see PyroSorc (however many to get this ability), Genie Warlock 3, Swashbuckler X to capitalize on one attack gaining tons of damage from both flames and Sneak Attack.

[MrStabby]

Hi everyone,

So my sister wanted to play a Pyromancer type Sorcerer character - and she wanted a cool ability to reflect that, sort of like a 'heating up' mechanic. My DM and I had a (quick!) think, and came up with the following:

''Each time you deal damage with a fire spell, add 1d4 to the damage roll. This die size increases for each successive spell that hits an enemy, to a maximum die size of d20. When the die reaches d20, you take half the value of the dice rolled as damage to yourself. This damage cannot be prevented. The die will automatically reset itself back to d4 if you deal no fire damage during your turn.''

Ok. So the idea is, your (fire) spells grow progressively more powerful - if they hit - but at 'max power' they will damage you, to counterbalance it. Now firstly, I understand the ability is terribly written - we wrote it on the fly, and I'm sure there must be a more concise and accurate way of writing that out. I mean, for example, 'each time you deal damage' was not meant to include single spells that do damage multiple times, such as Scorching Ray - but how do you write that out clearly?

But more importantly, the wording aside, is it balanced? Frankly, we found it difficult to judge. A Draconic Sorcerer for example, gets to add their Charisma modifier to their (insert element here) spells - which would almost always be +4 or +5. With our ability, the damage would only be (on average) +5 after three consecutive spell hits (when the die is a d10) - which seemed fairly balanced to us, as three consecutive hits is by no means guaranteed. Sure, the ceiling is a lot higher, but you've got to be lucky.

Anyway, what do you guys think? Overall, we like the idea of 'growing power', having an element of luck, and a risk/reward type system, as it all seems very 'Pyromancy' - but we'd genuinely love to know how balanced this sounds from any more experienced players. And, if it's sounding completely absurd, what might we do to change it, whilst sticking to the rough concept?

Thanks very much for reading!

So to the key questions - what level is this ability at and what other abilities will the class have?

[Forechosen]

Eek, massive apologies for missing so much! I went for a little nap :smallredface:

I'll try and reply to everybody!


Have you looked at KibbleTasty's phoenix Soul homebrew/update of UA?

I haven't, but I'll have a quick look now!


If you're solely comparing this feature vs. draconic then I understand the concern re: power level....

Hmm, all of what you've said is completely true - but I don't know, I suppose it just feels like it ought to be balanced to work at as many tables as possible, even though it never will be? I mean, you're absolutely right in that none of it really matters - as long as everybody is having fun. I just think it's worth trying to balance it as best as I can, within reason!

Regarding the spell levels 'heating up' different amounts, I actually really like this idea - I love the idea of higher level spells being more 'explosive'. What worries me is how annoying this might be to keep track of? You're already having to keep track of what die you're on. I know it's not a lot, but anything extra could potentially be a little annoying. I'm not sure, I do like the idea a lot!



How about this?

"Once on each of your turns when you deal fire damage with a spell, you gain a Flame Charge (insert better phrasing).......

Ahh see I like this idea too! But I don't know, I don't feel it represents the 'heating up' theme enough? It seems a little too controlled?

Honestly though I am really appreciated all this feedback, I don't want to sound dismissive!


I like this idea, but I'd also consider balancing it to having a total number of steps to maximum equal to your Proficiency bonus. So at 5th level, it unlocks the capacity for 1d8 to be your cap, before that it charges up over two rounds but caps at 1d6. With that adjustment, I'd hold on the self-damage until at least the d10 mark, as taking half damage every other round at levels 1-4 can be rough.


Hmmm, ok this is interesting, I'll have a think about this. I suppose at first glance, what I'm thinking is that - MrStabby explained above why this ability is potentially a little weak. Would we want to weaken it further by putting a cap on the heat?

I do like the idea though, it's always fun to 'unlock' things as you level up, and this would make it more exciting. I'll have a think!


So to the key questions - what level is this ability at and what other abilities will the class have?

Ok - so firstly, to give some context, we're all level three at the moment. Her character died at the end of last session, and she'd like this to be her new one. Also, the campaign is Rime of the Frostmaiden (I haven't read it, didn't want to spoil anything) - and the DM is taking it incredibly slow. We're on our.. I don't know, tenth session at the moment? Something like that. We do all like it slow though, I just mean to say we wont be reaching higher levels anytime soon at all.

We're thinking it would be a level one ability, as it would be pretty iconic for the subclass. However, we're open to changing that to level 6 if needs be.

The other abilities are pretty much from the 'Pyromancy' from Planeshift Kaladesh, with added Draconic Wings.

Essentially...

Level 1 - this ability, plus, she can take spells from any class so long as they deal fire damage. Such as Heat Metal, for example.
Level 6 - the ''Heart of Fire'' ability from 'Pyromancy'
Level 14 - Draconic Wings (well, actually, just some form of flight), my sister wanted this.
Level 18 - ''Fiery Soul'' ability from 'Pyromancy'

But with all that being said - we're not sure. As I said, we only gave it all a quick think. I wasn't even sure (at all!) about this first ability before I posted here.

Things I'm considering - 1). There are two damage abilities in that list, Level 1 and Level 6. Two seems like too many. However, heating up and having fire literally emanate from you sounds incredibly cool. But this is what I'm most concerned about.

2) The capstone is very, very boring. But, dealing with fire immune enemies isn't that rare, so I suppose it is important. It just doesn't make you go 'wow, exciting' does it? That being said.. we're level 3 at the moment, it's a little way off.

3) There's nothing defensive. I would have loved to have squeezed in the unarmored AC from the Draconic Bloodline, but.. where? It seems too much to tack on along with everything else at level 1. And too weak to stand by itself at level 6.

I can't stress enough how much all this is up for change though. But, well, that is the idea!

[MrStabby]

Ok - so firstly, to give some context, we're all level three at the moment. Her character died at the end of last session, and she'd like this to be her new one. Also, the campaign is Rime of the Frostmaiden (I haven't read it, didn't want to spoil anything) - and the DM is taking it incredibly slow. We're on our.. I don't know, tenth session at the moment? Something like that. We do all like it slow though, I just mean to say we wont be reaching higher levels anytime soon at all.

We're thinking it would be a level one ability, as it would be pretty iconic for the subclass. However, we're open to changing that to level 6 if needs be.

The other abilities are pretty much from the 'Pyromancy' from Planeshift Kaladesh, with added Draconic Wings.

Essentially...

Level 1 - this ability, plus, she can take spells from any class so long as they deal fire damage. Such as Heat Metal, for example.
Level 6 - the ''Heart of Fire'' ability from 'Pyromancy'
Level 14 - Draconic Wings (well, actually, just some form of flight), my sister wanted this.
Level 18 - ''Fiery Soul'' ability from 'Pyromancy'

But with all that being said - we're not sure. As I said, we only gave it all a quick think. I wasn't even sure (at all!) about this first ability before I posted here.

Things I'm considering - 1). There are two damage abilities in that list, Level 1 and Level 6. Two seems like too many. However, heating up and having fire literally emanate from you sounds incredibly cool. But this is what I'm most concerned about.

2) The capstone is very, very boring. But, dealing with fire immune enemies isn't that rare, so I suppose it is important. It just doesn't make you go 'wow, exciting' does it? That being said.. we're level 3 at the moment, it's a little way off.

3) There's nothing defensive. I would have loved to have squeezed in the unarmored AC from the Draconic Bloodline, but.. where? It seems too much to tack on along with everything else at level 1. And too weak to stand by itself at level 6.

I can't stress enough how much all this is up for change though. But, well, that is the idea!


So... how much is mechanics and how much is fluff?

Can we, for example add faerie fire to the spell list? How about refluffing stinking cloud as a smoke cloud? Sleet storm as cinder storm (OK the slippy ground makes less sense there).

Or is it just damage and blasting stuff?

If it is the former, and the character will be able to take advantage of casters being able to select the most appropriate action from their menu then the character will be a lot more powerful.

Also - in a more general sense of building a character, you could equally well homebrew a bunch of spells to build the fire theme whilst enabling more than damage (also helpful vs fire immune enemies)

[Forechosen]

So... how much is mechanics and how much is fluff?

Can we, for example add faerie fire to the spell list? How about refluffing stinking cloud as a smoke cloud? Sleet storm as cinder storm (OK the slippy ground makes less sense there).

Or is it just damage and blasting stuff?

If it is the former, and the character will be able to take advantage of casters being able to select the most appropriate action from their menu then the character will be a lot more powerful.

Also - in a more general sense of building a character, you could equally well homebrew a bunch of spells to build the fire theme whilst enabling more than damage (also helpful vs fire immune enemies)

Hmm, I'd say Sorcerer's have a pretty large spell list as-is.. we were thinking of just adding more fire spells specifically, just so she wouldn't miss out on awesome, very thematic spells such as Flame Strike.

As far as flavoring, I'm speaking for my sister a little here, but I think she'd be fine with a little bit, but not excessively? Stinking Cloud as Smoke Cloud makes complete sense.. but trying to reflavor Cone of Cold, for example, into a fire spell just sounds a little weird?

I mean she absolutely does just want to blast stuff. I think the other spells she's interested in are the mind-controlling side of things - Charm, Suggestion, etc. - because they fit into her vision of a fiery-devilish-tiefling character. So I reckon she'll be casting those a bit too, and, as you say, 'slightly' reflavored utility spells.

[cookieface]

It might be a little more mechanically complex, but what about something that takes advantage of Sorcery Points?

For instance (this is off the top of my head, so might be imbalanced):

"Heating Up: When you cast a spell that successfully deals fire damage, you immediately gain one sorcery point [per level of the spell maybe?]. This ability cannot cause you to exceed your maximum number of sorcery points.

Overheated: After you deal fire damage with a spell, you may spend a number of sorcery points up to [some number: proficiency, max sorcery points, half sorc level, whatever]. You may deal an additional 1d6 fire damage for each sorcery point spent. Each die can affect only one creature, but multiple dice can be spread across several targeted creatures, so long as all creatures were damaged by the spell. {This is to prevent nova-ing your fireball against a half-dozen creatures and doing something like 12d6 to all of them.}
If you spend more than two sorcery points when using this ability, you take half damage as the unleashed fire consumes you as well. This damage cannot be reduced by resistance or immunity, or any other means."

The issue is that you don't get sorcery points until level two, but that can be hand-waved because this isn't a published class; you're starting at level three anyways.

As an aside, the level six ability could tack on "Your cantrips that deal fire damage now are affected by Heating Up. When you cast a cantrip that successfully deals fire damage, you immediately gain one sorcery point."

[kingcheesepants]

Rather than having the extra damage increase by a die size each time, why not increase the number of dice and have them capped per prof bonus. So d4 at 1-4, d6 at 5-8, d8 at 9-12, d10 at 13-16 and d12 at 17-20. Have the number of dice increase to a max of +3 and anything after that deals half to the caster.

So in effect it would look like this turn 1 cast firebolt for 1d10+1d4 damage, turn 2 1d10+2d4, turn 3 1d10+3d4, turn 4 1d10+3d4 and 3d4/2 to caster. At level 5 your firebolt would do 2d10+1d6. This gives a nice bonus that will scale with level and doesn't get too crazy.

If you don't want the damage to cap out quite so quickly, you can incorporate some of the other suggestions about only letting leveled spells increase the damage and then cantrips can maintain the heat but not make it hotter. So turn 1 you cast burning hands to get the extra d4 and then all your firebolts after that have the d4. If you cast burning hands (or scorching ray or whatever) again you get another d4 to a max of 3d4. Leveled spells increase the number of dice by one, cantrips maintain the current dice and failure to cast a fire spell lower the dice by one.

[MrStabby]

Rather than having the extra damage increase by a die size each time, why not increase the number of dice and have them capped per prof bonus. So d4 at 1-4, d6 at 5-8, d8 at 9-12, d10 at 13-16 and d12 at 17-20. Have the number of dice increase to a max of +3 and anything after that deals half to the caster.

So in effect it would look like this turn 1 cast firebolt for 1d10+1d4 damage, turn 2 1d10+2d4, turn 3 1d10+3d4, turn 4 1d10+3d4 and 3d4/2 to caster. At level 5 your firebolt would do 2d10+1d6. This gives a nice bonus that will scale with level and doesn't get too crazy.

If you don't want the damage to cap out quite so quickly, you can incorporate some of the other suggestions about only letting leveled spells increase the damage and then cantrips can maintain the heat but not make it hotter. So turn 1 you cast burning hands to get the extra d4 and then all your firebolts after that have the d4. If you cast burning hands (or scorching ray or whatever) again you get another d4 to a max of 3d4. Leveled spells increase the number of dice by one, cantrips maintain the current dice and failure to cast a fire spell lower the dice by one.

If you were to go down this route, I would suggest something like he Aberrant Mind's level 6 ability to efficiently cast from sorcery points. Being able to continuously lay down a barage of low level spells would be important if only levelled spells were to empower the ability.

[kingcheesepants]

If you were to go down this route, I would suggest something like he Aberrant Mind's level 6 ability to efficiently cast from sorcery points. Being able to continuously lay down a barage of low level spells would be important if only levelled spells were to empower the ability.

Yeah being able to cast fire spells with sorcery points equal to the spells level would certainly help longevity. I think doing it so that only leveled spells power it up and you can cast said spells with SP works pretty well balance wise. You get a solid boost but it all comes at a price. Capping it at 3 before the blowback starts makes it a lot more relevant than having it go up 6 levels before it's dangerous but it's still pretty controllable, you either stick to casting cantrips after getting the bonus damage or you hold off on a fire spell for a turn. Or you simply take the risk and cast fireball even if it's gonna do 3d6 damage to you because sometimes it's worth it to hit a bunch of enemies. Upping the damage die with your level also allows it to be meaningful throughout your game. Doing a d4 or d6 of extra damage at level 15 isn't really super relevant but a d10 is a worthwhile boost at that stage.

[Amnestic]

I decided to codify the subclass ideas I liked into a proper document with obvious inspiration from the suggested OP's concept.

https://homebrewery.naturalcrit.com/share/j01cY7MCyRcu

1st level is the heat die ideas I tossed around.
Also a set of thematic spells, of course, every sorcerer subclass gotta have those.
6th level feature is minor defense vs. fire/cold and a pseudo-fire shield while you have a heat die active.
14th isn't flashy but it is efficient, downgrading immunity to resistance (which you can then further remove with the Elemental Adept feat if you so choose).
18th deletes Overheat damage from being a factor with immunity to fire damage (a reasonable capstone) and gives you a free metamagic on any fire damage spells, with the option to add a second one at-cost on top of it, which I think is a good way of showing fire mastery.

"Are you concerned about frontloading heat die as a first level feature?" No, it's specialised enough that if they are being a fire-caster then they're either sticking with pyrosoul or multiclassing into something like wildfire druid (MAD and also thematically that works, so go nuts).

[kingcheesepants]

One more thing that I didn't note about changing the extra damage die from one d4 up to 1d20, to a scaling with level multiple of the same die. Is that a if a 3rd level sorcerer is hit by 3d4 damage he is hurt meaningfully but he's not gonna die (just from that) but he very well may die from a d20. On the other end an 18th level sorcerer can take the d20 without much fuss but 3d12 is at least a little more threatening. That's in addition to the fact that the damage scales up faster, is more level appropriate in general and is quicker to blow up in your face (forcing you to be a bit more strategic and balance it a little more carefully).

Take a quick look at the stats
3d4: min 3 max 12 average 7.5
3d6 min 3 max 18 average 10.5
3d8 min 3 max 24 average 13.5
3d10 min 3 max 30 average 16.5
3d12 min 3 max 36 average 19.5
1d20 min 1 max 20 average 10.5

The max damage of 3 dice outpaces the max possible with 1d20 at the 3d8 mark (which would happen at level 9). And the average is exactly equal at the 3d6 mark (the level 5 boost). The minimum damage beats a single d20's minimum from the very beginning. If you want to get real crazy you can have a level 20 capstone boosting it up to a d20. 3d20s max is 60 and the average is 31.5. Which is a fairly crazy amount of damage but hey it's your level 20 feature you'll probably use it for one fight so why not go nuts.