Gelatinous Cube

Location Dungeon Levels 3–4
Damage 84–85
Notes Destroys equipped armor when it hits
Gelatinous Cubes not only deal a ton of damage, their hit destroys your Armour. It's a good idea to remove your Armour when on Dungeon Levels 3–4 for this reason. Note that Gelatinous Cubes appear as squares that take up the entire hallway, and can be easy to miss if you don't know what you're looking for.
Compare Gelatinous Cube to other Creatures
Cyclops Ettin

Related

Lands of Lord British

Page 2
Win the Red Gem in The Castle of the Lost King and obtain a vehicle that can cross water.

Gelatinous cube

Location Dungeon Levels 3–4
Notes Destroys equipped armor when it hits
Gelatinous cubes not only deal a ton of damage, their hit destroys armor. You can't equip new armor in a dungeon, so this can be extremely problematic. Your best bet is to use Ladder spells to get past them, and/or have high Stamina so they can't hit you easily. Note that Gelatinous cubes appear as squares that take up the entire hallway, and can be easy to miss if you don't know what you're looking for.