A fan favorite, and a monster that always seems to get some sort of reaction whether it be abject horror or elation, is the Gelatinous Cube. It has a presence that is simultaneously intimidating and ridiculous, because if you really think about it it’s basically just a big sentient jell-o. The more seasoned adventurers, however, know how difficult it can be take on this enemy. In the Monster Manual the Cube is listed as a challenge rating of 2; which means a healthy party should be able to rid themselves of it fairly quickly, but where it lacks in battle prowess it makes up for it with its natural abilities.
The Gelatinous Cube uses its blindsense to detect when a potential meal is near giving it the opportunity to hide itself to create a trap. They are naturally transparent making it incredibly difficult if not totally impossible to spot, unless of course remnants of its last meal still linger inside of it. Once in range the Cube engulfs their meal trapping them, this is where the real threat comes in. When engulfed the enemy can no longer breathe, is restrained, and takes periodic acid damage. They have the opportunity to try and escape but adventurers that usually come across the cube early on have a tough go at it. Such a fight can be surprisingly hectic with every member of the party flailing about determining the best course of action: do we continuing attacking, do we save Fred, do we just leave and hope for the best. It’s always a fun monster to use and it brings out some memorable moments in a campaign.
The Dungeoneer's Journal 