couldn't help myself from messing around some more
you could utilize the kirbyness to your advantage and have them appear uber cuddly and suddenly open there grimacing mouths and freak the hell out of the player
also function over form points, it better have 4 legs at the moment if it is 2 it seems impossible to move, and going with an eye monster mightn't actually be the best idea unless it has something else like giant razor sharp claws, because lets face it if a giant eye ball monster comes upto you besides freaking you out and bumping into you, or even crying on you, it won't be able to do much, whereas a giant mouthful of teeth that could bite your head off that's another thing entirely
also here is a quick 3D model I just slapped together in moments and colour reduced to show you what it would look like from iso view
sounds interesting is this side scrolling engine different than this. what you've implied is an isometric diablo-esque game?
and oh okay, wasn't entirely sure whether anime was intentional or not, although horror in that style is possible, and alot less effort to sprite in so it may be a consideration. but a happy combination could work, even just rendering them like these simplified to get into your game fast, but make sure they are flexible enough that you can detail and polish later if you want a more detailed and gritty art style. just another possible suggestion
and the idea of having something visible sloshing around etc is a decent one but I'd recommend saving it for another monster "too many ideas" = potential to pursue each idea separately, and not trying to cram them all in to one, or trying and then ditching the idea completely because it doesn't ultimately fit with the one you are doing. just some advice