Epedemic, at least when triggered by an “On (whatever)” appears to target an enemy, but affects the caster, thus possibly debuffing your creatures.
Also, I had a Skellie Sniper in the arena with a gem of Death Siphon that had cast on kill and start of battle. He killed all of his allies at the start of round 4, which would have been fine by me, except… He then cast it in himself. Wish I’d had the presence of mind to screenshot that for my collection. It was pretty funny.