I think this 100-pointer's just having fun and enjoying himself. He's just transforming into whatever the hell he wants, whenever he feels like it, lol. I almost want him to win.
And, as much as I hate that Kazuo guy (the one with only half his suit on) for raping that alien and apparently everything else... he really is a badass. Not only did he easily defeat that thing that tore up a bunch of people in Gantz suits while buck naked, he knows when to walk away. Pretty cool dude if he wasn't a rapist. I'm sure he's gonna die (I've read it before but can't even remember).
I couldn't help but get a kick out of the part about the bull ogre in the omake, where it says "Here, we see it attack small insect-like creatures with machine guns." Lol, it's bad but still funny.