Stolen from Mister RPGPundit, 5e version. Normal and monstrous. My PCs had fun with this, they actually didn’t kill it because they thought it was too cool to kill! (cue 1970s disco music). A disco cube is a mutated gelatinous cube that uses music to trap its prey.
Normal Disco Cube
Disco Cubes are gelatinous squares measuring anywhere from four to twelve cubic-feet. Their otherwise transparent form flashes with bright, multicolored lights in a pulsating pattern. Whenever they move, an unsettling musical sound that is also highly dance-able is produced; the combined sound and lights also have a hypnotic effect. Disco Cubes are nocturnally active, hunting from about 9pm until nearly dawn. They are completely still and unresponsive for most of the day (unless attacked). When still, they do not produce any lights or music, being very difficult to detect and having a high probability (50%) of surprising someone.
Take a standard gelatinous cube and add the following Otto’s irresistible dance as an additional action (DC 12). The spell targets all creatures within 30 feet that can hear and see it.
Monstrous Disco Cube
Huge Ooze, Unaligned
Armor Class 6
Hit Points 162 (12d12 + 84)
Speed 20 ft.
STR DEX CON INT WIS CHA
18 (+4) 3 (-4) 24 (+7) 1 (-5) 6 (-2) 1 (-5)
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, prone
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 8
Languages —
Challenge 5 (1,800 XP); Proficiency Bonus +3
Ooze Cube. The cube takes up its entire space. Other creatures can enter the space, but a creature that does so is subjected to the cube’s Engulf and has disadvantage on the saving throw. Creatures inside the cube can be seen but have total cover. A creature within 5 feet of the cube can take an action to pull a creature or object out of the cube. Doing so requires a successful DC 15 Strength check, and the creature making the attempt takes 14 (4d6) acid damage. The cube can hold only one Huge, two Large, or up to four Medium or smaller creatures inside it at a time.
Transparent. Even when the cube is in plain sight, it takes a successful DC 15 Wisdom (Perception) check to spot a cube that has neither moved nor attacked. A creature that tries to enter the cube’s space while unaware of the cube is surprised by the cube.
Actions
Multiattack. The cube uses Heavy Beats and then makes two Pseudopod attacks.
Pseudopod. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 14 (4d6) acid damage. If the target is a Large or smaller creature, it is grappled (escape DC 14). Until this grapple ends, the target is restrained, takes 14 (4d6) acid damage at the start of each of the cube’s turns, and the cube can’t use this pseudopod to attack another creature.
Heavy Beats. The cube targets all creatures within 30 feet of it that can see or hear it. Each target begins a comic dance in place: shuffling, tapping its feet, and capering for the duration. Creatures that can’t be charmed are immune to this effect. A dancing creature must use all its movement to dance without leaving its space and has disadvantage on Dexterity saving throws and attack rolls. While the target is affected by this spell, other creatures have advantage on attack rolls against it. As an action, a dancing creature makes a Wisdom saving throw to regain control of itself. On a successful save, the effect ends.
Engulf. The cube moves up to its speed. While doing so, it can enter Huge or smaller creatures’ spaces. Whenever the cube enters a creature’s space, the creature must make a DC 15 Dexterity saving throw. On a successful save, the creature can choose to be pushed 5 feet back or to the side of the cube. A creature that chooses not to be pushed suffers the consequences of a failed saving throw. On a failed save, the cube enters the creature’s space, and the creature takes 14 (4d6) acid damage and is engulfed. The engulfed creature can’t breathe, is restrained, and takes 28 (8d6) acid damage at the start of each of the cube’s turns. When the cube moves, the engulfed creature moves with it. An engulfed creature can try to escape by taking an action to make a DC 15 Strength check. On a success, the creature escapes