Use Magic Device and Mnemonic Vestment

[udalrich]

I have a player asking about using Use Magic Device with Mnemonic Vestment to cast a spell that is not on his spell list with a UMD check.

The relevant parts of the rules are

Use Magic Device:

Use a Scroll: Normally, to cast a spell from a scroll, you must have the scroll's spell on your class spell list. Use Magic Device allows you to use a scroll as if you had a particular spell on your class spell list. The DC is equal to 20 + the caster level of the spell you are trying to cast from the scroll. ... This use of the skill also applies to other spell completion magic items.

Mnemonic Vestment:

If the wearer is a spontaneous caster, once per day she may use a spell slot to cast a spell from a written source (such as a scroll or spellbook) as if she knew that spell. The spell must be on her spell list, the same spell level or lower than the expended spell slot, and the same type of spell (arcane or divine) as the spell slot expended.

I don't think it will work for a Sorcerer casting a Paladin spell, since UMD says nothing about changing the arcane/divine nature of the spell, while the vestment explicitly requires that to match.

I am less clear about a Sorcerer casting a Bard spell. The arcane/divine problem is not present. One one hand, UMD says "as if you had a particular spell on your class spell list". On the other hand, this is talking about directly casting it from the scroll and explicitly extends it to only spell completion items. Since the vestment does not consume the scroll, it is not a spell completion item.

If it does not work by the rules, would a house rule to allow it to work be a bad idea? I suspect that allowing arcane users access to other arcane spells would not be a serious problem, but I can see arcane/divine combos being problematic. Mixing 3/4 and full caster spell lists could also be a problem: I'm not sure that I want to see a Magus casting Righteous Might or Harm, even if it is only once a day.

[Monster Ronster]

That is a very good question. UMD lets you use magic items you don't otherwise qualify for, even a non-caster can use scrolls and wands with it. That tells me that UMD is intended as a powerful skill. Rather than the Use Scroll part of it, I would say that Emulate A Class Feature would be the appropriate function. In this case, the user would be emulating the ability to cast divine spells if an arcane spellcaster, or vice-verse. One spell per day isn't going to break the game, imo, but it allows creative users greater versatility.