Not counting anything like the Wraiths I'd say... Breadbugs are like a perfect mix of cute, funny, and cool in gameplay concept. Being a play on the concept of carrying items to base by having a creature who actually carries things to their own base and plays tug of war with your Pikmin is really fun. Not to mention I like how they fit into the general world of PNF, such as how they masquerade as Dwarf Red Bulborbs, just a really neat idea honestly.

I'm also a fan of Jellyfloats, purely from a design perspective, colors are really pretty and the sounds they make are calming and I like where you encounter them. Cannon Beetles are also fucking awesome in how they integrate into the gameplay itself, either being one of the most hazardous enemies in the game or your easy way into slaughtering a lot of potentially dangerous monsters.

Ujadani as the cracked insane person answer though.