Crimson/Magenta Slime (Large)

Ambush. The slime can latch to ceilings, and can use this to get the drop on targets. When a creature passes below the slime, it can drop on top of them and use its Engulf.

Gluttonous Ooze. The slime takes up almost its entire space. Other creatures can enter the space, but a creature that does so is subjected to the slime’s Engulf and has disadvantage on the saving throw.

Creatures inside the slime can be seen but have total cover.

A creature within 5 feet of the slime can take an action to pull a creature or object out of the slime. Doing so requires a successful DC 17 Strength check, and the creature making the attempt takes 18 (3d10) acid damage.

The slime can hold only one Large creature or up to four Medium or smaller creatures inside it at a time.

Transparent. Even when the slime is in plain sight, it takes a successful DC 17 Wisdom (Perception) check to spot a slime that has neither moved nor attacked. A creature that tries to enter the slime’s space while unaware of the slime is surprised by the slime and can be targeted by its Engulf. 

Pseudopod. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 18 (3d10) acid damage.

Snare. Ranged Weapon Attack: +6 to hit, reach 20-60 ft., three creatures. Hit: 11 (2d10) acid damage. The hit creatures must make a DC 13 Dexterity (Acrobatics) or Strength (Athletics) check, otherwise will be pulled 15 ft. closer to the slime. 

Engulf. The slime moves up to its speed. While doing so, it can enter Large or smaller creatures' spaces. Whenever the slime enters a creature's space, the creature must make a DC 16 Dexterity saving throw.

On a successful save, the creature can choose to be pushed 5 feet back or to the side of the slime. A creature that chooses not to be pushed suffers the consequences of a failed saving throw.

On a failed save, the slime enters the creature's space, and the creature takes 18 (3d10) acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 35 (6d10) acid damage at the start of each of the cube's turns. When the slime moves, the engulfed creature moves with it.

An engulfed creature can try to escape by taking an action to make a DC 17 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of the slime.