Multiattack

The sapphire jelly makes two freezing slam attacks.

Freezing Slam

Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 10 (2d6 + 3) bludgeoning damage plus 10 (3d6) cold damage.

Engulf

The jelly moves up to its speed. While doing so, it can enter a Medium or smaller creature's space. Whenever the jelly 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 jelly. A creature that chooses not to be pushed suffers the consequences of a failed saving throw. On a failed save, the jelly enters the creature's space, and the creature takes 10 (3d6) cold damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 21 (6d6) cold damage at the start of each of the jelly's turns. When the jelly moves, the engulfed creature moves with it. A sapphire jelly can have only one creature engulfed at a time. An engulfed creature can try to escape by taking an action to make a DC 15 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of the jelly. Alternatively, a creature within 5 feet of the jelly can take an action to pull a creature out of the jelly. Doing so requires a successful DC 15 Strength check, and the creature making the attempt takes 10 (3d6) cold damage.