Both are in their strongest incarnations.
Battle is in Hogwarts
win condition: KO or death
Prep is 1 day
Voldemort and Gandalf team up to fight the Deadly Alliance of Shang Tsung and Quan Chi from Mortal Kombat
Bonus fight takes place in Shang Tsung's Palace in MKD.
Win condition: KO or Death
Edit: DA has access to the Dragon Kings Army