Why not Have a guy that looks like a super hero residing in the basement of a very big mansion with a lot of guys wearing “Laser swords” (Don’t deal enough damage to kill you instantly) and the basement is a huge “battlefield” littered of other “survivors” corpses then he could say “Huh? Another one comes down… Heh you don’t look so weak so I am gonna be good to you. Now before we get the fight started let’s shake hands for good sportsmanship and honor…” If you shake hands he kills you instantly saying “Killer spark…” and if you don’t he will get mad and attack.
-A big quantity of HP and defense would be a early end-game boss
-And the guy would have very powerful laser or energy related attacks as well as melee attacks and before every attack he will say “Killer” before the name of the attack ex.
Killer Beam!.
-The guy will obviously be called Killer man and its description would be something like this
"He is a man wearing what it looks like a classical super hero suit that makes him look muscular but something about him makes you doubt his intention… Whether it’s the place where he resides or the fact that he does not seem to belong in this world…
-The guy parodies Destroy man from No More Heroes. I dunno why but most bosses from that game fit in a post apocalyptic world if you ask me… xD