well.
as cromox said go Object Editor --> Buffs/Effects
then there re human/orc/undead/nightelf/special folder
take the special folder
in the special folder are 2 other folders. one is Buffs and one is Effect.
now open Effect. There should be the "Rain of Fire (Effect)". Click on it and change the Graphic - Effect to something else.
But as cromox said there are only blizzard, rain of fire and a sheep animation that fall down from the sky (and you can download some from hive), that means if you change the graphic -effect to .. lets say a paladin model, the paladin wont fall down from sky, he appears on the ground for some seconds