What save, if any?

I have a very old fashioned bad guy, and that means his fortress has a special rule: any time you cast a spell with a spell slot, you forget that spell until you finish a long rest. Should that effect have a save, and if so, which? Befuddlement is Int, Modify Memory is Wisdom.

Well it depends on what it means to forget in this case. Is it because their knowledge of the spell is violently pulled out of their mind? It would be wisdom to resist such a force. If it’s because their ability to comprehend their spells is muddled, intelligence would be to format and reinforce how those spells function. Finally, charisma would be for sheer force of being, which would help against having having your soul or existence being modified in some way.

Quote from ClassicCharismaCaster >>

Well it depends on what it means to forget in this case.

Well, the fundamental effect is that they're subject to the influence of prior editions of D&D :)

TBH, might be a Charisma save, that’s the only saving throw that would fit for having your fundamental reality screwed with.

I would say that this is something messing with the ability which gives them the spell; Wizards would forget how to understand their own runes, a sorcerer might have a mental block on how they cast it, and a bard would forget the words.

As such, I would have the save be with their spellcasting ability. That way, they have a decent chance of passing, and you won't favour one spellcaster over the other (EG a wizard who dumped charisma compared with a bard who maxed it).

While I'm not a fan of that effect, because it could seriously affect encounter balance in ways you don't expect, I would agree with Thoruk and say the save uses the caster's spellcasting ability score, whatever it is.

EDIT: One twist you could throw in is to base the DC on the level of the spell slot used, e.g. "the DC is equal to 12 + the level of the slot being used,"  which would make higher level spells more of a gamble and lower level spells safer.

If you want the spell to affect different targets with different kinds of magic, you could give the player the choice by wording the ability as "The target makes an Intelligence, Wisdom, or Charisma saving throw (their choice) to resist the effect..."

Quote from ThorukDuckSlayer >>

I would say that this is something messing with the ability which gives them the spell; Wizards would forget how to understand their own runes, a sorcerer might have a mental block on how they cast it, and a bard would forget the words.

As such, I would have the save be with their spellcasting ability. That way, they have a decent chance of passing, and you won't favour one spellcaster over the other (EG a wizard who dumped charisma compared with a bard who maxed it).

 That's my feeling too, whatever their justification for casting spells is should be the thing that is impacted by the effect. However I do think Stabbey has a point and it could have a big impact on balance you don't expect. It's also likely to make the spell casters feel unfairly targeted compared to the martial characters who presumably will have no similar effect

Quote from Stabbey_TC >>

While I'm not a fan of that effect, because it could seriously affect encounter balance in ways you don't expect, I would agree with Thoruk and say the save uses the caster's spellcasting ability score, whatever it is.

EDIT: One twist you could throw in is to base the DC on the level of the spell slot used, e.g. "the DC is equal to 12 + the level of the slot being used,"  which would make higher level spells more of a gamble and lower level spells safer.

 And that's sort of similar to how save DC in 3.5e was based on the level of the spell.

So a paladin might only get to smite 1/day in 5.5, ouch.

I like the above poster with it being a save based on casting stat. Another way could be a skill check - arcana for wizards, religion for clerics, performance for bards, etc. and just hope the poor eldritch knight does their best. Though quite a few have expertise in places where it could make the check much easier, if that’s what you’re going for.

Quote from Stabbey_TC >>

While I'm not a fan of that effect, because it could seriously affect encounter balance in ways you don't expect

The PCs are 16th level, I've long since given up on encounter balance being calculable in a meaningful way.

Save using spellcasting ability, definitely

Dont know if id make the dc go up with spell level or not...

Also, would it be spell level (complexity of spell) or slot level (how much power you put into it). If its spell level, then at least players could figure out that a somewhat solution is to take a low level spell and upcast it.

If its slot level then its hard to use high level spells and upcast low level spells.

If you want to give the martial players a moment to shine, this would do it.

Quote from Pantagruel666 >>

Quote from Stabbey_TC >>

While I'm not a fan of that effect, because it could seriously affect encounter balance in ways you don't expect

The PCs are 16th level, I've long since given up on encounter balance being calculable in a meaningful way.

 Oh, 16th level. Then just go nuts. They’ve got plenty of spells to choose from. It will be a fun challenge for a session or two. I’d just telegraph the effect somehow, so each spell turns into a tactical choice of, do I cast this now, knowing I probably can’t do it again?