On the subject of Packrat Palooka, I found him difficult to bag alive firstly because I didn't want to risk killing him and had a look at a walkthrough (which had the same strategy Nate posted), however, after playing through the game again I found that it's much easier to just pound into him with whatever hurts him (let him stay up on his 'stage', doesn't matter) and by the time he's on just less than a quarter health, he will jump off and come after you himself, and that's basically when you hit him with the zappflies and thudslugs, then bounty him. Works pretty well for me.
And about a Slig based FPS... In my opinion it'd work better as a faster paced Gears of War third person style game. I think the clunking of your robotic legs would be better felt in that style.
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