Witch ability with Rune Giant with Div
 

So a player was facing Div and I used the witch ability to use Rune Giant's bad stuff as a curse, and they lost.. now if Div's bad stuff is to use the first curse at the top of the stack, does Rune Giant's bad stuff (as a curse that was used) take effect instead?

Re: Witch ability with Rune Giant with Div
 

While using the witch's ability does enact bad stuff as though it were a curse, the monster and its bad stuff don't gain any lasting new properties. That is to say that once the bad stuff has been applied as a curse resulting from the use of the witch's ability, the bad stuff on the monster card immediately returns to its state of just being bad stuff on a monster card.

For the "top curse" it would be the first card labeled as a curse that would be applied as a result of that combat loss.

Re: Witch ability with Rune Giant with Div
 

Mathgeni is correct. Use the first actual Curse card you come to; any other effect that might briefly have been treated like a Curse doesn't count.