Decay

[Kuritza]

Indie lich killed a whole troop of my skinshifters with Winds of death once, the mass-decay spell. He cast it twice, so nearly all my skinshifters started decaying, and by the time they broke through lich's skellies they started dying from old age.
Once WoD inflicted heavy casualties on my LA Man crossbowmen, too. Useless in small in fast combats, it gets quite dangerous in epic battles with 200+ units on each side.

Single-target decay is not useless enough though.

[Fantomen]

It´s pretty ok against Abysia with their short lifespans