That Robo-Mouse,even though it's not a boss,is something that scared the crap out of me,and still does to this day. It's more of the execution than the design it's self,so far there hasn't been anything putting pressure on you besides the bosses. And you go to the Stagnant Swamp and you see that-OH CRAP ITS A GIANT ROBOTIC MOUSE RUN FOR THE HILLS!! And it's almost impossible not to get hit by it first time through. (Unless you activate a glitch,which most people wouldn't.) And how does that mouse kick you out? Physhic powers? Throws Wario through the cieling? HOW?!?! But yeah,Robo-Mouse is spoopiest boss.