Build help to maximize Mizzium Apparatus payoff?

[Setharious]

Recently a friend of mine and I discovoered the magic item, Mizzium Apparatus, and have a mild obsession over it trying to figure out the best way to build it. Long story short for what the item does is that it lets you cast any spell from your classes spell list even if you do not know it or have it prepared, and needs to be attuned to a sorcerer, warlock, or wizard. To cast a spell you need to succeed on an arcana check, DC = 10 + 2 x Spell Level. If you fail it goes wild with its own personal table.

A big thing for me to note is if you multiclass into druid until level 2, you can get circle of stars druid which lets you enter a special dragon constellation state that makes it impossible to roll under a 10 on arcana checks, which with 20 int and expertise in arcana, I believe you can't fail the DC at any spell level. Beyond that, I am just struggling with finding additional synergy, or particularly good spells lists.

So how would you build it? Would you try to get access to all spells with multiclassing or are there certain lists not worth it? Thanks for the help!

[Amnestic]

Stars Druid 2/Knowledge Cleric (for arcana expertise and cleric spell list) 1/Wizard [x] is the most common build I see for it, though you can swap level amounts for class features as desired, you only really need 1 level in each to get it, and Wizard is there for the int-focus since you're boosting it for arcana rolls anyway.

Of the other classes:
Sorcerer and bard don't have enough unique spells to warrant needing 13 cha (in addition to 13 wis+int) for a dip.
Paladin spells are nice, but it slows down your spell slots/ASIs and requires 13 cha.
Ranger unique spells aren't worth the slowdown.
Artificer has no unique spells.

You could exchange Knowledge for a different cleric domain if you get expertise elsewhere (such as skill expert feat) but you still probably want to take a cleric level for their spell list.

As far as wizard subclasses, it's dealer's choice, though since you're getting medium armour+shields from your wis-classes I'd probably lean away from bladesinger.

[Dualight]

A big thing for me to note is if you multiclass into druid until level 2, you can get circle of stars druid which lets you enter a special dragon constellation state that makes it impossible to roll under a 10 on arcana checks, which with 20 int and expertise in arcana, I believe you can't fail the DC at any spell level.

Let's do some simple calculations to see if this is entirely true: DC= 10+2(spell level), so the maximum DC is for a 9th level spell, giving DC= 10+2(9)= 28.
with 20 INT and Expertise in Arcana, the bonus at level 20 is 5(INT)+ 12(Expertise)=17. THus, you would need a minimum roll of 11 to succeed for a 9th level spell, which means that even dragon constellation doesn't do the trick.
However, if you can get your hands on a tome of clear thought, which allows your INT to rise to 22 (or if you keep playing beyond 20th level for those Epic Boon replacing ASIs that increase the cap to 30), the bonus to Intelligence (Arcana) checks becomes +18, right at the threshold for 9th level spells from the mizzium apparatus.

That said, since the bonus fall only 1 point short of the DC(assuming that the mizzium apparatus is the only magic item you are guaranteed to have), any effect that increases your Arcana checks at all will be enough to guarantee success. Since Stars druid always gives guidance, non-concentration spells are effectively guaranteed if you are in a situation where you can get away with casting guidance on yourself.

An interesting thought experiment, to be sure. I wonder if there are other permanent ways to increase your Arcana bonus that I am not thinking of.

[Setharious]

That said, since the bonus fall only 1 point short of the DC

From what I understand, RAW, a nat one does not currently force a failure to ability checks, meaning that that single point of difference will be made up for during the roll. So I guess you can't fail, depending on whether or not your DM uses critical failures of ability checks or not.

[Amnestic]

An interesting thought experiment, to be sure. I wonder if there are other permanent ways to increase your Arcana bonus that I am not thinking of.

Luckstone (Uncommon) is probably easiest. +1 to saves and all ability checks.

You can also lean on other people - for guidance, bardic inspiration, flash of genius, etc. - it's a worthy investment for since it's a 9th level spell.

Though, if you go wizard 17 you probably won't need it that often either, since I expect most of your 9ths will be spent on Wish which is wizard-native.

Luckstone is the 'easiest' solution though, and at 17+ it should not be an unreasonable thing to acquire, though it does take a valuable attunement slot. You can always just attune to it until you use your 9th and then swap out for something else though.

[Dualight]

From what I understand, RAW, a nat one does not currently force a failure to ability checks, meaning that that single point of difference will be made up for during the roll. So I guess you can't fail, depending on whether or not your DM uses critical failures of ability checks or not.

Thing is, the DC is 28, not 18, the assumption already is that the dragon constellation Starry Form from Stars druid makes the lowest possible die value 10.
To make even 9th level spells an absolute certainty, a bonus of +18 is needed.


Luckstone (Uncommon) is probably easiest. +1 to saves and all ability checks.

You can also lean on other people - for guidance, bardic inspiration, flash of genius, etc. - it's a worthy investment for since it's a 9th level spell.

Though, if you go wizard 17 you probably won't need it that often either, since I expect most of your 9ths will be spent on Wish which is wizard-native.

Luckstone is the 'easiest' solution though, and at 17+ it should not be an unreasonable thing to acquire, though it does take a valuable attunement slot. You can always just attune to it until you use your 9th and then swap out for something else though.

Luckstone, of course! I keep forgetting about the effect that one has on Ability checks.
Thinking on it, the Lore bard's Peerless skill would allow for a guaranteed +18 as well. And since only a single use is needed for the desired effect, leaving CHA at the 13 needed for the multiclass does not inhibit the combo. It would result in a build meant to optimise for just the one thing, but it would need no magic items other then the mizzium apparatus.

[Setharious]

Thing is, the DC is 28, not 18, the assumption already is that the dragon constellation Starry Form from Stars druid makes the lowest possible die value 10.
To make even 9th level spells an absolute certainty, a bonus of +18 is needed.

I understand now, and I was a fool.

[Bphill561]

These builds have come up in the past, and there are builds floating around. The Vedalken Race is right in the Ravnica book, you cannot skip them. They can get Knowledge Arcania and with Tireless Precision, they get to add a +1d4 to every roll using the skill. If you are not using Tasha's rule edits, they also have a baseline +2 Int, +1 Wisdom which is also useful.

Along the same lines, you could always go with the peace cleric for your cleric subtype. They can use their emboldening bond on themselves and additional targets equal to their prof. bonus with # of uses equal to their proficiency bonus. It lets you add a +1d4 to one attack, save, or ability check (arcana check) once a round for 10 minutes.

Stack both of these and add guidance in if you have the time or are out of combat.

If unearthed arcana is on the table, the Lore Wizard is another way to get expertise in any knowledge skill you have. It ironically also can heavily manipulate spells and eventual duplicate spells from another list once per long rest. Although you can do just as well with an Skill Expertise Feat.

I always thought it would be interesting, although less efficient, to take it another direction. If you are heading for a high level game I would be tempted to try this out on an Arcane Trickster Rogue with 12 levels. Reliable Talent would give you the auto 10 on knowledge arcana and rogue can give you the skill expertise. 8 Levels of other full spell casting classes would get you up to 6th level spells, DC 22. Your proficiency bonus will already be +5 at level 13 when you start multiclassing, doubling to +10 with expertise. You should be able to swing an Int of 14 by that point since you need a 13 to multiclass anyway. This puts you at a DC22 without rolling or having any race/class/magic item bonus skill bonus items. Again this is totally different because you are playing a rogue not a full caster, but you would have quite a bit of versatility spell wise. Maybe go Wizard 4/Cleric 2/Druid 2 to get whatever subclasses you want.

Edit: Someone just mentioned the Quandrix Primer magic item in another non-related thread. Uncommon magic item that adds 1d4 to Knowledge arcania checks after you roll and decide to expend a charge. Can we doe +4d4 then with the other listed abilities above? The luckstone is probably better though overall, and not from Strixhaven.