Cantrip that buffs an ally's attack--how many dice should it be?

[LordShade]

My players may gain the assistance of a Sulatar artificer in an upcoming adventure, and I want the artificer to primarily focus on enhancing the party's weapon attacks. One tool this NPC may have is a cantrip that would add damage to a weapon attack, ala Booming Blade, except the caster enchants an ally's weapon with it.

The cantrip would be cast using a normal action, probably with a 30' range, and affects a weapon held by an ally. The ally makes a normal weapon attack as part of their Attack action on their turn, and gets the bonus damage if the attack hits. To my knowledge there are plenty of effects that add bonus dice to one's own attack (BB, Improved Divine Smite, cleric Divine Strikes/Blessed Strikes, etc) but there are few that enhance an ally's attack. Those that do (Crusader's Mantle, Elemental Weapon, Holy Weapon) aren't single-hit effects. This cantrip would be something like Holy Weapon except it only works on one swing.

If I wanted this action to be roughly comparable in efficacy to a normal cantrip, how many dice should it add to the attack? Assuming Firebolt is the baseline cantrip, the d10/120' gets knocked down to a d8/60' or thereabouts for having a better damage type and a rider of some kind. I'll assume range is a wash since this could theoretically be cast on an ally's bow or arrow, as well as a sword. Damage, well, I think this cantrip is actually worse because the damage is delayed to an ally's turn instead of doing the 4d10 or whatever right away on the caster's turn. The only advantage would be if the ally had a higher attack modifier than the caster.

If this cantrip does 1d8 fire per step, it's pretty clearly worse than Firebolt because of the delayed damage. Does that imply that a d12 would be more reasonable? Another idea is that it's more like Eldritch Blast, and enchants up to four weapons for 1d8 or whatever per step. Then it's more like an aura, and would give several players the chance to roll extra dice.

I realize that as the DM, the balance is kind of immaterial because I'm in total control of how much DPR I want to add to the party. I'm just curious about what would be "balanced" if this was a player spell.

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For players reading this, would it be fun for you if there was an NPC spamming a Booming Blade effect on you from time to time?

[Dork_Forge]

If this is going to be NPC only, then I'd encourage you to look at the Drake wardens reaction, which I think is 1d6 elemental.

[Anymage]

D12, scaling at cantrip rate, contingent on the first attack hitting sounds reasonable. Letting it trigger off multiple hits would be problematic scaling, but running off the fighter's attack bonus instead of your own sounds okay when you realize the two should be pretty close to each other.

Alternately, you might want to drop those dice down to d6s or even d4s, drop the first one (akin to the bladetrips), and let one target within close range make an attack with whatever weapon they gave handy. This strikes me as something to be careful with as letting the rogue take out of turn attacks (and thus extra sneak attacks) is a sizeable boost. If that's not a concern in your campaign, an NPC with a support ability that lets the PC attack sounds like the sort of NPC support that keeps the spotlight on the players.

[Dork_Forge]

D12, scaling at cantrip rate, contingent on the first attack hitting sounds reasonable. Letting it trigger off multiple hits would be problematic scaling, but running off the fighter's attack bonus instead of your own sounds okay when you realize the two should be pretty close to each other.

D12s seems a bit much since damage-only cantrip like Fire Bolt and Eldritch Blast peak at d10s. Even more so if you keep in mind that it's additive, not primary, damage that would presumably multiply on a crit.

[Kane0]

Neat idea! I'd give it 1d8 or 1d10 bonus damage (scaling with an extra die at 5, 11 and 17) to the next attack that hits within 1 minute (no concentration), but range touch.

[Amnestic]

D12s seems a bit much since damage-only cantrip like Fire Bolt and Eldritch Blast peak at d10s. Even more so if you keep in mind that it's additive, not primary, damage that would presumably multiply on a crit.

Toll the Dead does d12, contingent on the enemy already being damaged. Wouldn't be the worst thing if you did something similar.

D8 or D10 for a ranged weapon attack, d12 for melee (due to the added danger).

[Dork_Forge]

Toll the Dead does d12, contingent on the enemy already being damaged. Wouldn't be the worst thing if you did something similar.

D8 or D10 for a ranged weapon attack, d12 for melee (due to the added danger).

With a condition and lacking the ability to crit.

It wouldn't be the end of the world or break the game, but if you're going to make something may as well do some semblance of balancing with the game.

[Amnestic]

With a condition and lacking the ability to crit.


Right, and firebolt can crit at 120ft away. If firebolt were a melee cantrip (firefist?) would it still be d10? Or would it gain a boost because it's a melee attack vs. a ranged attack?

[Dork_Forge]

Right, and firebolt can crit at 120ft away. If firebolt were a melee cantrip (firefist?) would it still be d10? Or would it gain a boost because it's a melee attack vs. a ranged attack?

We don't have an existing basis, but I don't see why it would. You have to get into melee, but you can also take advantage of prone and aren't susceptible to cover or disadvantage from a hostile within 5 ft.

[Boci]

We don't have an existing basis, but I don't see why it would. You have to get into melee, but you can also take advantage of prone and aren't susceptible to cover or disadvantage from a hostile within 5 ft.

The only melee cantrip we have is Shicking Grasp, which is only 1d8, but is electricity not fire damage, and also prevents a hit enemy using their reactions, so it could go either way as to what a melee ranged fire cantrip would look like.

[elyktsorb]

Right, and firebolt can crit at 120ft away. If firebolt were a melee cantrip (firefist?) would it still be d10? Or would it gain a boost because it's a melee attack vs. a ranged attack?

Poison Spray is a 10ft cantrip that does a d12 of poison damage but has a con save for it.

Also Primal Savagery is a melee cantrip that deals 1d10 acid damage.

Seems like they are very hesitant to give the d12 to a cantrip without heavy qualifiers of some kind.

[Joe the Rat]

d8s or d10s. You could go d10 if there are no rider effects, but any sort of rider (reaction block, heal block, speed reduction, mockery) drops you a die size.

Something else to look at is instead of scaling, have it persist: duration of a minute, good for 2 hits at 5, 3 hits at 11, etc. If you need to restrict, have it limit to one active casting, a la light and shillelagh. That would mitigate a lot of nova concerns.

[stoutstien]

If it's a npc why even waste the effort making it a cantrips and just make it an action that does what you want?

Working of that I'd make it a modified help action.

[Theodoxus]

If it's a npc why even waste the effort making it a cantrips and just make it an action that does what you want?

Working of that I'd make it a modified help action.

This was essentially my thought. The only other thing I would suggest is, if crits are a concern, to just have the cantrip add a static amount of damage. Say, 5, 6, or 7 per tier. (Depending if you're wanting to replicate a d8,d10, or d12.)

[Mastikator]

If it's a npc why even waste the effort making it a cantrips and just make it an action that does what you want?

Working of that I'd make it a modified help action.

TBH agreed. Just give the NPC crusader's mantle but make it fire damage. Or give him elemental weapon but he always chooses fire damage.

Or let him turn one of the player's mundane weapons into a flametongue for a minute once per long rest. That could be his special ability.

[LibraryOgre]

1d6, of a specified type.

Rationale:

Searing Smite and Wrathful Smite both provide 1d6 bonus damage; fire and psychic, respectively. They also have special effects; continuing damage and fear. They are self-range bonus actions; this would be a close-range, and I assume Standard Action.

Stripping the special effects and upping the action cost are, IMO, equivalent. Increasing the range goes along with the drop in level. In this case, I would keep it as a concentration until expended option... I cast it, and you flail about until you hit, doing +1d6 damage. If it takes you a while to hit, I can keep the spell up, and do other things. Otherwise, I cast it again.

Thunderous Smite should be 2nd level.

[LordShade]

d8s or d10s. You could go d10 if there are no rider effects, but any sort of rider (reaction block, heal block, speed reduction, mockery) drops you a die size.

Something else to look at is instead of scaling, have it persist: duration of a minute, good for 2 hits at 5, 3 hits at 11, etc. If you need to restrict, have it limit to one active casting, a la light and shillelagh. That would mitigate a lot of nova concerns.

What do you mean by nova concerns?

I don't have a strong opinion on the d8 vs d10 or d12. But just to keep it simple (and this is the Sulatar from Eberron) let's say that the cantrip will be fire damage. And I'm imagining that it should be castable on a bow/arrow (there's a bow ranger in the party), so I'll assume the 120' range for Firebolt is a wash. How do you weight the damage happening later in the round (or the next round) versus it happening immediately? If the damage is delayed to another character's turn, this cantrip seems clearly worse than Firebolt, at least to me.

In other words, is the effect only taking place after a delay a heavy enough qualifier for a d12?

[LordShade]

TBH agreed. Just give the NPC crusader's mantle but make it fire damage. Or give him elemental weapon but he always chooses fire damage.

Or let him turn one of the player's mundane weapons into a flametongue for a minute once per long rest. That could be his special ability.

All of these and @stoutstien's are great ideas.

The "why bother with complicating it" is mostly out of curiosity about what people think would be balanced if this was a player spell. I'm fully aware that as the DM I can just give any special ability to any NPC that does whatever I want.

[windgate]

I have concerns running this idea as a cantrip. I think you are better off introducing this as a leveled spell. Namely, due to the concerns that DMPC's typically create. If weapon enhancement spells are the only spells the NPC can actually cast, there is no risk of your players feeling overshadowed (and you are not metagaming against yourself when designing content).

Have you looked at the Battlemaster Fighters Commander Strike Manuever? All that really needs is a damage type change.

Instead of a cantrip how about the following leveled spell.

Elemental Weapon (1st Level):
(Concentration), Duration one minute

Touch one weapon you can see. Until this spell end, the first time this weapon hits a target each round the target is inflicted with additional damage from one the following types (X, Y , Z) This spell ends when the weapon is no longer held by the same person as when the spell was cast.

1st Level 1d10
Each additional spell Level adds 1d10 more damage.

You then have your NPC follow up each later round of combat with a modified version of the the aid action (that only applies to weapons affected by the spell)

[Boci]

Stripping the special effects and upping the action cost are, IMO, equivalent.

Is it though? Think of ray of sickness for example. 2d8 damage, save or be poisoned. Are you telling me you think its fine as a bonus action, 2d8 damage, if we remove the poison effect? What about the reverse. If Misty Step was an action, but also allowed you to force a will save or frighten some creatures, would people like it as much? Thunderrous Step does exist, and its a level higher in addition to being an action, but its also triple the range, allows you to take another creature with you, and 3d10 thunder damage to creatures within 10ft of you.

[LibraryOgre]

Is it though? Think of ray of sickness for example. 2d8 damage, save or be poisoned. Are you telling me you think its fine as a bonus action, 2d8 damage, if we remove the poison effect? What about the reverse. If Misty Step was an action, but also allowed you to force a will save or frighten some creatures, would people like it as much? Thunderrous Step does exist, and its a level higher in addition to being an action, but its also triple the range, allows you to take another creature with you, and 3d10 thunder damage to creatures within 10ft of you.

I was making a specific example, not a general rule.

[Frogreaver]

Assuming we are going with applies on first hit with weapon then it should probably be d6 and scale at normal cantrip rate. Multiple attacks, boost accuracy of such an effect.

Honestly I’d probably scale it by keeping it a 1d6 and cantrip scaling lets it affect more ally’s.

[Vegan Squirrel]

How would an optimizing PC look to use this cantrip? I'd imagine one of the benefits to delaying the damage would be transferring it to a character who can attack with advantage. If the rogue or paladin is usually attacking with advantage, then their attacks are more likely to hit than the spellcaster's cantrip attacks. This is good (and increases the odds of a crit a little), but the delay could prove to be a detriment anyway (especially if the cantrip requires concentration). The fight could be over before that player's turn, their expected target could disengage or die, the PC in question could take enough damage to fall unconscious or change their tactics, etc.

All in all, it seems reasonable for a cantrip. I think a d10 is fine, but I wouldn't object to a d12 (especially if the cantrip requires concentration). Another option would be to make the cantrip add 2d6 damage, then increase by only 1d6 at 5th, 11th, and 17th levels. It would be a good cantrip early on, but slowly fall off from there. At higher levels, it would still be worth it for certain attacks that are highly likely to land.

If the cantrip lasts until one of the target's attacks hits, then I'd probably just use 1d6 since the damage is closer to guaranteed. But that's not how the OP presented it as working.

[LordShade]

How would an optimizing PC look to use this cantrip? I'd imagine one of the benefits to delaying the damage would be transferring it to a character who can attack with advantage. If the rogue or paladin is usually attacking with advantage, then their attacks are more likely to hit than the spellcaster's cantrip attacks. This is good (and increases the odds of a crit a little), but the delay could prove to be a detriment anyway (especially if the cantrip requires concentration). The fight could be over before that player's turn, their expected target could disengage or die, the PC in question could take enough damage to fall unconscious or change their tactics, etc.

All in all, it seems reasonable for a cantrip. I think a d10 is fine, but I wouldn't object to a d12 (especially if the cantrip requires concentration). Another option would be to make the cantrip add 2d6 damage, then increase by only 1d6 at 5th, 11th, and 17th levels. It would be a good cantrip early on, but slowly fall off from there. At higher levels, it would still be worth it for certain attacks that are highly likely to land.

If the cantrip lasts until one of the target's attacks hits, then I'd probably just use 1d6 since the damage is closer to guaranteed. But that's not how the OP presented it as working.

This is the sort of reasoning I had in mind. My benchmark was 4d10 damage at the cost of using an action (Firebolt). If I get only 4d6 damage by spending the same action, AND the damage is delayed to someone else's turn, that's clearly a bad trade. As you point out, the only situation in which delaying the damage to someone else's round (in between the monster can get in an attack and do damage, whereas a Firebolt might have killed it) is if the gain in accuracy from casting it on the raging barbarian with a +3 sword outweighs the loss in time.

@windgate, I appreciate your concerns about DMPCs. All I can say is that I'm a veteran DM from the 2e days and I am just not one of these "DMPC hogs the spotlight" DMs :) My campaign is in Eberron and I've made clear to the players that the PCs are the heroes and the centerpiece of the campaign, and there are no Elminsters and Drizzts for the world to fall back on.

Moreover, the players will be controlling the actions of this NPC in combat if it joins the party. The players already have two NPCs accompanying them, a Qaltari drow scout and a thri-kreen, which they manage in combat. Both have modified abilities from the base statblocks. The drow is roughly CR1, and the thri-kreen is CR2. The players are level 6.

Part of the reason I don't want to give the NPC spell levels and slots is that I don't want any player cognitive load to go towards resource tracking on a story/support NPC. Basically I want the NPC to have a simplified, mostly-resourceless decision tree. That's why I'm exploring this as a cantrip, but it could just as easily be a resourceless special ability. I will say to the players, "this NPC is basically a magewright, but he has some exotic cantrips that are not known in Khorvaire." When this NPCs turn comes around, I don't want the players to spend more than a few moments thinking about its action, but also don't want its abilities to be so simple that it just autoattacks every round. I want to give the players an interesting choice to make, but not one that's overwhelming. Another interesting cantrip might be the Rune Knight's fire shackle ability. That would mean the artificer can every round, either add a large amount of damage to a player attack or inflict a single-target stun with low damage on a single enemy. Interesting and useful choice.

I really like many of the ideas listed in this thread. A simple 1/SR "your weapon is now a flametongue", the Commander's Strike (Fire) idea, and the Drakewarden idea is actually pretty perfect. My original inspiration for this NPC was something like the character Lucca from the old Chrono Trigger game, where she had an ability that buffed another character's sword strike with fire damage. The resulting damage was higher than either character could have done on their own, but required the two to coordinate their turns to act together.

[Boci]

So a situational way to abuse this, if it were a cantrip, would be to have multiple 1st level mages / CR 1/2 magic users, all cast it on the same character, who then attack with advantage / some other ability. Assassin could be especially good here. Not sure if this warrants specifying it doesn't stack.

[Amnestic]

So a situational way to abuse this, if it were a cantrip, would be to have multiple 1st level mages / CR 1/2 magic users, all cast it on the same character, who then attack with advantage / some other ability. Assassin could be especially good here. Not sure if this warrants specifying it doesn't stack.

A character can't benefit from the same spell more than once at a time, that's just part of the general spellcasting rules.

[Vegan Squirrel]

So a situational way to abuse this, if it were a cantrip, would be to have multiple 1st level mages / CR 1/2 magic users, all cast it on the same character, who then attack with advantage / some other ability. Assassin could be especially good here. Not sure if this warrants specifying it doesn't stack.


A character can't benefit from the same spell more than once at a time, that's just part of the general spellcasting rules.

Furthermore, that wouldn't really be broken even if it were allowed. It could take advantage of buffing just one character's attack roll and giving them advantage (maybe they even have Elven Accuracy and Lucky to further that advantage), but in the end it's no more damage than if each mage had landed a fire bolt on their turn instead of buffing their ally. It's still a cantrip of damage per cast, either way.

[Osuniev]

I think if the buff lasts UNTIL an attack land, then it should be less than 1d10.

Yes, damage now is better than damage later, but on the other hand, an attack WILL eventually land, whereas a character casting Firebolt might just waste their action.

It's tempting to think "well it's basically equivalent to casting Firebolt if the mage to hit bonus is similar to the Fighter's."
But that's a pretty big if : if you make that cantrip open to players, they are plenty of smart ways to optimize it, beause everything that improves accuracy now only needs to apply to one character instead of two :
- Bardic Inspiration,
- Bless,
- Help action (from a familiar),
- magic weapon (the spell),
- magic weapons (the items),
- consumable ammunitions,
-True Strike,
- Precision Attack,
- Reckless Attack
- Flanking
- BUILD decisions (increasing the primary stat of the martial will actually increase the damage output of the caster, which now free to pick a feat with his ASI instead of increasing his primary stat)

Plus the caster chooses on who they cast it, so they will generally cast it on someone that is not restrained, not blinded, can reach the target, can risk engaging in melee, etc...

All of this are advantages to using this spell rather than Firebolt. Of course they are potential downsides :
- sometimes the caster will be the one that has the good positioning/bless/bardic inspiration/etc....
- if the martial is much later in initiative order, it's going to delay damage by a lot
- everything that reduces the accuracy of one single attack (like a Parry reaction) now reduces the impact of the cantrip as well,
...but then the caster can just do something else. So you should look at the balance of the spell in situations where it shines (if they are relatively common), because that's when it will be used.


I think this is a really good idea ! It emphasizes synergy and teamwork, gives the caster interesting strategic choice whist making the martial feel awesome. But it doesn't need to do 1d10 damage, even less 1d12, to be worth using !

[LordShade]

Yeah--I was imagining that it only enchants the weapon for one attack. If the attack misses, the effect goes away, like Booming Blade. Under these conditions I think a d12 is more and more appropriate. Besides, my players never have a chance to roll d12s.

I agree that if the effect persisted until a weapon attack successfully lands, the damage should be lower than d10.

[Mastikator]

If it's d12 then I'd go with "their next attack before the end of their next turn". I'd probably give it a 30 feet range and make it an action. IMO cantrips have no business being bonus actions (or reactions).

[Anymage]

Moreover, the players will be controlling the actions of this NPC in combat if it joins the party. The players already have two NPCs accompanying them, a Qaltari drow scout and a thri-kreen, which they manage in combat. Both have modified abilities from the base statblocks. The drow is roughly CR1, and the thri-kreen is CR2. The players are level 6.

Part of the reason I don't want to give the NPC spell levels and slots is that I don't want any player cognitive load to go towards resource tracking on a story/support NPC. Basically I want the NPC to have a simplified, mostly-resourceless decision tree. That's why I'm exploring this as a cantrip, but it could just as easily be a resourceless special ability. I will say to the players, "this NPC is basically a magewright, but he has some exotic cantrips that are not known in Khorvaire." When this NPCs turn comes around, I don't want the players to spend more than a few moments thinking about its action, but also don't want its abilities to be so simple that it just autoattacks every round. I want to give the players an interesting choice to make, but not one that's overwhelming. Another interesting cantrip might be the Rune Knight's fire shackle ability. That would mean the artificer can every round, either add a large amount of damage to a player attack or inflict a single-target stun with low damage on a single enemy. Interesting and useful choice.

I really like many of the ideas listed in this thread. A simple 1/SR "your weapon is now a flametongue", the Commander's Strike (Fire) idea, and the Drakewarden idea is actually pretty perfect. My original inspiration for this NPC was something like the character Lucca from the old Chrono Trigger game, where she had an ability that buffed another character's sword strike with fire damage. The resulting damage was higher than either character could have done on their own, but required the two to coordinate their turns to act together.

Since she's an NPC and NPCs can have powers that PCs don't, I'd be tempted to give her an at-will ability where everybody within a certain radius of her gets to add a dice to all their weapon attacks until her next round. Either everybody with 30' gets +1d4, or everybody within 10' gets +1d6. You can fluff it as her having focused on being really good at that one spell instead of having focused on a wider variety of spells known/slots available. This makes her useful and tactically interesting, but also avoids complexity and gets to keep the spotlight more on the PCs. Give her that and a basic Firebolt for when she wants to stay at range, those two powers should be plenty.

Edit to add: the dice sizes mentioned above could be safely raised by one size in your average group. They were lowballed because a party optimizing around number of attacks to capitalize on per attack damage bonuses could get tricky.

[kazaryu]

you should be perfectly fine having it be normal cantrip damage (i.e. d10 with an extra die per level). in fact you're right in that the delay to adding it to an ally makes it even weaker than most attack cantrips, so you're definitely safe. if this is where you're going you might also consider having this NPC be able to cast things like magic weapon and elemental weapon, or divine favor.

[Oramac]

If it's a npc why even waste the effort making it a cantrips and just make it an action that does what you want?

Working of that I'd make it a modified help action.

This.


The "why bother with complicating it" is mostly out of curiosity about what people think would be balanced if this was a player spell. I'm fully aware that as the DM I can just give any special ability to any NPC that does whatever I want.

I'm actually surprised nobody has brought up true strike yet. Not as an actual use case, but for comparison. The whole "I use my action now for [xyz thing] later" concept. Admittedly, using the cantrip to add damage, as you suggest, is most certainly better than true strike; especially if the buff persists from turn to turn. But how much better? If I'm the wizard and I have this cantrip and some other damaging cantrip, what would make me use this over my own damage?

For this reason, I would suggest that the cantrip needs low-ish damage and a shorter range (perhaps 1d6 or 1d8 and 30 feet) but comes with a decently powerful rider. A wis save vs Frightened would work. Or maybe a cha save vs one-round banishment? IDK. For that matter, a wis save vs one round of petrified would make it almost universally useful.

[Theodoxus]

I'm actually surprised nobody has brought up true strike yet. Not as an actual use case, but for comparison. The whole "I use my action now for [xyz thing] later" concept. Admittedly, using the cantrip to add damage, as you suggest, is most certainly better than true strike; especially if the buff persists from turn to turn. But how much better? If I'm the wizard and I have this cantrip and some other damaging cantrip, what would make me use this over my own damage?

For this reason, I would suggest that the cantrip needs low-ish damage and a shorter range (perhaps 1d6 or 1d8 and 30 feet) but comes with a decently powerful rider. A wis save vs Frightened would work. Or maybe a cha save vs one-round banishment? IDK. For that matter, a wis save vs one round of petrified would make it almost universally useful.

OTOH, making it ranged but not requiring LOS/LOE because friend, would be useful - especially as an DMPC, but even on a PC, I could definitely see a case where I would use it while ducking behind a wall, door, box, etc. Staying out of immediate combat but still contributing beyond something like Bless or similar (thinking more holistically than just as a wizard) would be a godsend for some character concepts. Not everyone wants to play the 'in your face' style caster...

[MrStabby]

From a balance perspective, if its 1 attack in the next turn, I think a D12 is fine.

Damage can be lost to overkill. You lose the choice of targets. A spell that incapacitates your target robs you of your action as well.

You exchange that for some flexability in choic of target, probably damage type, chosing a tool with a good hit bonus.



I have some reservations about it. Buffs can often be a bit difficult in this way. If there are similar...ish characters then buffing one of them can open up a gulf of effeciveness between them. This is especially true if there are things like rolled stats - one character has a higher attack bonues, it becomes natural to buff that character over the one with the smaller bonus and you drive up the gulf between characters.

[Oramac]

OTOH, making it ranged but not requiring LOS/LOE because friend, would be useful - especially as an DMPC, but even on a PC, I could definitely see a case where I would use it while ducking behind a wall, door, box, etc. Staying out of immediate combat but still contributing beyond something like Bless or similar (thinking more holistically than just as a wizard) would be a godsend for some character concepts. Not everyone wants to play the 'in your face' style caster...

Good point. I think I'd still require line of sight, but even then you could just lean around a corner, cast, and duck back behind the corner.

Overall, I really like the idea. It just needs polish and playtesting.

[Yakk]

Charged Weapon + Artificer Cantrip
Range: 30 ft
Target: 1 weapon or piece of ammunition
Duration: 1 round (concentration)
Casting Time: 1 action
Effect: The next time the target weapon or ammunition is used to make an attack, the attack gains advantage. If the attack hits, it deals an extra 1d8 lightining damage.
At higher levels: At level 5 the damage increases to 2d8, 3d8 at level 11 and 4d8 at level 17.

I'm arguing it shouldn't be a pure "you deal more damage" but something slightly more interesting. Here, we grant advantage and a damage boost.

I agree this is a strictly better spell than True Strike, but True Strike is a garbage spell, so that comparison is useless.

Also, the (concentration) requirement I have above could be removed and it still wouldn't be overpowered. With concentration it is definitely a low-optimization ability (even if it can still be used usefully in a less stressful encounter).

My True Strike variation is self only and deals 1d12 and requires concentration - but on the True Strike case, the delay (of 1 round) is worse, as well as the restriction to the spell caster (who presumably is less deadly and gets less benefit from the advantage than you can get with this spell).

With (concentration) I could even boost the spell to have a duration of 1 minute, and remove the ammunition clause (which is just flavor - you can just boost the weapon), and add in a bonus action that lets you refresh the charge. It would add a mini game of "whack the artificer" to break concentration. Might be getting too strong however.