gelatinous cube

If memory serves, somewhere there is a section in the rules for Oozes, Puddings, Jellies, etc.

Am I remembering wrong?

Module has a gelatinous cube in it. I can create it but I could swear Rolemaster has one somewhere.

But then, it has been 30 years...

The only one that I can think of is the Caustic Slime. You should be able to find it in Creatures & Treasures.

Yeah, I'd start with the Caustic Slime as a baseline and then modify from there.