I guess, only Exploding Dwarf can make more damage in one turn, but it only works in some rare situations.
Cursed Slimeball seems to be even more powerful when used with Crypt Mancer + Undead Priest, so all monsters have -2 HP. On the other hand, this card belongs to the Death splinter, the weakest one for maxed cards and Earth/Water with Prince Rennyn/Nymph or Valnamor/Mermaid Healer/Sea Genie have a lot of HP. It will make Death more competitive, but I think it won't make it an easy win for Death. Maybe it will just make people play less this boring Cocatrice + Brownie + Ooze line-ups.