Ickis, Krumm & Oblina
These three are so complementary to one another that I couldn't just pick one over the other two, and they're technically all the same vaguely defined species anyway, so let's pretend they count as just one entry. Nickelodeon's "Aaahh!! Real Monsters!" told the story of three students attending a school for monsters in the sewers beneath a garbage dump, where they were taught by the perpetually (and lovably) furious Gromble in the art of scaring humans, which is later revealed to keep the entire monster race from fading out of existence. The show was loaded with creative creature designs, but our three central characters were appropriately the most iconic and in some ways the most bizarre.
Panicky, geeky Ickis is often thought of as "the" main character of the show, though wasn't focused on significantly more. Rounding out the excessive oddness of his two classmates, Ickis is often mistaken by humans for some sort of unusual "bunny," but has the power to menacingly increase his size, which makes him a "loomer" in their terminology.
The brainy, responsible one of the trio, Oblina was also probably the most surreal
monster in the whole series, with huge lips on a flexible wormlike body, usually held in a candy-cane shape. Her scaring tactic was definitely my favorite; she would reach into her mouth and pull out her own guts
to show people, or in some cases flip completely inside-out into a pulsing, slimy mess!
The lovably simple-minded Krumm might actually be my favorite of the three, and in my opinion the one genuinely unnerving
design, thanks to his eerily human anatomy. Lacking a head, he carried his own eyeballs around in his hands, a feature the show had endless fun playing with - he could, of course, see through them no matter where they were. His specialty was his horrendous, unbearable stench, which may sound more gross than scary, but when a hairy humanoid head with stubby limbs and disembodied eyes jumps around a corner to stink
at you, you're bound to have a bit of a Lovecraft moment.