There is a whole family of monsters in D&D that is just ooze. Now, to be fair, all those oozes are different colors and do different and invariably awful things to adventurers:
- melting armor,
- melting faces,
- consuming you whole.
In the end though, they're just semi-formed blobs of, well...blob. Now before all the ooze lovers go off and defend their viscous favorites - I'm not coming down on them. I just want to point out that D&D writers and designers have enough imagination to make congealed ick into a whole species of dangerous animals.
So on one end of the spectrum, we have the simple ooze; on the other end of the spectrum we have things like the arboreal grappler (Tome of Beasts, Kobold Press, 2016). It's an orangutan with arms that curl up like ropes and wrap up PCs like fuzzy constrictors. Sit back for a minute and revel in the weird of that creature.
In my scenario, The Serpents of Hailwood, I absolutely revel in the weird. I may or may not have also made it a zombie. Want your PCs to face an undead ape-thing with snaky arms? Of course you do. I also incorporated the strange and foreboding moon blooms in this scenario - and included their stat block in the text. Remember though, while I can freely use the names of the monsters in the Tome of Beasts, you'll have to buy it if you want the details.