Mayuri tends to fight alone and/or kill off his comrades while trying to get his "test subject," plus he may also just get others to do his dirty work for him and not even bother to fight at all. And once the cure is administered, they make full recoveries from the effects of the poison and can go back to fight (assuming they don't have other injuries). Hmm, then again, tthat only seems to work for Mayuri's cure... 

Man, it's hard to find a villian who isn't super powerful or dead.