For those that dont know what ??? Arceus is look on bulbapedia.
My question is: Curse (in Gen IV) is a ??? type move. Does this mean ??? Arceus get STAB from it?
Arceus will not get STAB from it. Curse is a non-damaging move, so no Pokemon get STAB. However, if a ??? Arceus uses Judgement, it will be ??? type and STAB.