Dalamar
Adventurer
I think it's pretty clear that you use a single stat for the spellcasting of all your classes if you're a multiclass spellcaster. I'd say one reason for this is the fact that if you kept your casting stats separate, with just moderate abilities, you could add lots of bonus spell slots/spells prepared to the lower spell levels by multiclassing (Galen, for example, wouldn't only have added the slots granted by the witch class, but would've also gained one bonus slot/prepared spell for 0th and 1st level spells thanks to 13 Wis).Arcana Unearthed said:Spellcasting: If a character has two spellcasting classes, add the spell slots and spells readied at one time totals together. If the two different classes use different key ability scores for their spellcasting, the player should simply choose which of the abilities to use (once made, the choice can't be altered)
It doesn't, however, change the related stat for stuff like the witchery manifestations (which aren't spellcasting).