# Which spellcasting ability is used when a multiclass character casts a spell through Mizzium Apparatus?

Let's say we have a character with this build: Cleric 1/Druid 1/Warlock 1/Wizard X, and it has a Mizzium Apparatus.

You can attempt to cast a spell that you do not know or have prepared. The spell you choose must be on your class's spell list and of a level for which you have a spell slot, and you must provide the spell's components.

You expend a spell slot to cast the spell as normal, but before resolving it you must make an Intelligence (Arcana) check. The DC is 10 + twice the level of the spell slot you expend to cast the spell.

On a successful check, you cast the spell as normal, using your spell save DC and spellcasting ability modifier.

Our character uses the Mizzium Apparatus to cast a Druid spell they did not prepare. Since they have multiple spellcasting abilities, which one is used to determine the spell save DC and attack roll modifier? Is it determined by the spell list to which the spell belongs, or is it the player's choice? What about spells that appear on multiple spell lists, such as Cure Wounds?

• Related, potentially a duplicate: "Which spell save DC to use for a Staff of the Magi for a multiclass Eldritch Knight/Sorcerer?" Nov 5, 2021 at 17:45
• This is a different question since a Druid Spell may not be on other class lists. It would seem that the intended mechanic would be a spell DC for a class for which the spell is on the class spell list. Nov 5, 2021 at 18:05
• @TigerGuy the answer goes into detail about that case, and the conditional is identical. Nov 5, 2021 at 18:16
• @Akixkisu, I don't think it is identical, because the MA says " The spell you choose must be on your class's spell list and of a level for which you have a spell slot." Nov 5, 2021 at 18:22
• The more I read the item description, the more I'm convinced the writers didn't think about multiclassing at all when writing it. Nov 7, 2021 at 6:07

### Use the spellcasting ability of the class with which you cast the spell.

The rules for spellcasting in case of characters with more than one class states (emphasis mine):

Each spell you know and prepare is associated with one of your classes, and you use the spellcasting ability of that class when you cast the spell.

Per description, Mizzium Apparatus allows the caster to access to all spells in all their spell lists. This is equivalent, for example, for a Wizard to have all the spells that they can cast in their spellbook, as they know them. Since for divine casters the spells are always known, this magic item allows to try the casting of an unprepared spell.

The multiclassing rules are hence straightforward to apply. If you cast a spell from the Druid list, you must use the spellcasting ability of the Druid, if you cast a spell belonging to the Wizard's list you must use the INT ability and so on. In case you cast a spell that belongs to more than one list, you choose from which list (and hence the ability to use) you are selecting the spell.

A further motivation for using the multiclass rules for spellcasting relies on the item description:

You expend a spell slot to cast the spell as normal, [...]

which means that you are not casting the spell through the item$$\^\dagger\$$, but you are spending one of your slots. This means that you can upcast a Cure Wounds, for example.

Let's consider some cases for clarification.

• Cast Entangle: this spell belongs to the Druid list only, hence you are forced to use the Druid spellcasting ability.
• Cast Cure Wounds: this spell belongs to both Cleric and Druid list. In this case, you should decide with which class you cast Cure Wounds. Both Druids and Clerics have the same ability (WIS) for casting, so from a numerical point of view it doesn't change anything, but for example if you are a Life Domain cleric choosing the Cleric's list grants you some advantages.
• Cast Thunderwave: this spell belongs to Druid, Cleric (Tempest domain) and Wizard lists. In this case you have to choose to use WIS or INT as spellcasting ability for setting the DC. Beside choosing the highest value, you may consider other factors ( such as the Destructive Wrath from Tempest domain, or the Sculpt Spells if you are an Evocator, when you reach levels higher than 2, for example).
• Cast Cause Fear: this spell belongs to both Wizard and Warlock lists. In the former case you must use INT as spellcasting ability, in the latter CHA.

$$\^\dagger\$$ A spell cast in this way can not be considered hence to be more than one class' spell at the same time, because it is not cast via the magic item.

• The rules you quote say: "Each spell you know and prepare" and ones cast through the Mizzium Aparatus are neither known nor prepared. Notably, spells cast from other magic items can be considered to belong to two classes at once. Nov 7, 2021 at 19:10
• @Exempt-Medic That's not true: Cleric and Druid spells are always known. Per description, MA allows you to access to all spells in your spell lists. In case of Wizards, it means that they can access to all spells that they can cast, as all these spells are in the spellbook, hence known. In case of Sorcerers or Warlocks, they can access to all the spells as they know them. In case of Cleric, Druids and other divine casters, they can cast an unprepared spell. Moreover, you are not casting the spell from the magic item, but you are using one of your spell slots. Nov 8, 2021 at 7:32
• @Eddymage your edit clears that up. You should check your text again, there are a few places where it seems like you missed words like "you choose from which list (and hence the ability to use) you are selecting the spell." Some of these are quantifiers with multiple possibilities, so I hesitate to edit them. Nov 9, 2021 at 15:19
• @Akixkisu Sorry, I do not understand what you mean: I am not a native English speaker, what words are missing (or not properly used) in that sentence? Nov 9, 2021 at 15:34
• Maybe overcomplete, but if you chose between Warlock and Wizard you also choose between using a Pact Magic spell slot or a regular one.
– Erik
Nov 12, 2021 at 8:39