and Jelly 
This leaves:
Biscuit
Checkered
Custard
Glowing
Halloween
Ice
Robot
Sketch
Snot
Snow
Split
Sponge
Strawberry
Zombie
Halloween, Robot, and Zombie all have potential to be cool. Checkered, Glowing, and Split tend not to be too spectacular. Ice and Snow are iffy, generally depending on artist. Strawberry might be cool, while after the Biscuit Gelert, I'm not sure another (plain) Biscuit pet would be appreciated. Sponge and Sketch have both lost a lot since the revamp, though they might be cool if done well. Custard and Snot are Custard and Snot.