As long as Extant didn't attack right away, there is a very slight chance DD could win. You see, Extant is composed purely of chronal energy. When DD faced Waverider, he was able to cancel out his chronal energies in order to negate the attack WR planned to use on him (the second time around.) So the chance is potentially there, imo.
However, all it would take for Extant to win here is an Entropy Rift, so I'd give him the nod. Meh.
Originally posted by john allerdyceNot trying to be rude, but you're very incorrect. Due to the events/alterations of Zero Hour, Doomsday ended up being saved before he was destroyed by Entropy:
an entropy rift wouldnt kill doomsday. hes already been dropped in entropy and survived just fine.
This retcon took place during the Doomsday Wars arc (which, ironically enough, is the version you specified in this thread. heh.)