The Probiotics buff you need to fight Doomsday in Doomed Metropolis is stripped from you once you are defeated and respawn (whether revived by another player or revive at a respawn point). The timer on the Probiotic does not reset. This means you're pretty much out of the fight until your Probiotic timer resets. Also, if you are defeated and Doomsday is repelled you do not get Feat credit if you participated.
