Honestly I feel like the killer robot could be a lot more in this game, heck even a playable character, I haven't thought of any stats but I feel it would be cool. Or instead you could find him in a top secret lab of some sort to activate him as a boss fight or possibly (maybe there could be a method to) make the robot join your party.
#The Killer Robot
leaden finch
Also as a side note, maybe a mutator that'll make the world doomed to end by him in a certain time frame, with the only way to find him being that lab I was talking about.
simple sorrel
i feel like you should elaborate on how would the killer robot be playable without just being like either a god mode or getting old in 2 minutes due to the comically slow speed
leaden finch
Maybe the robot could have an overdrive mechanic which boosts his speed for a bit
dusty root
Just give the killer robot homing missiles. That'll increase it's difficulty.