Concrete Golem

Immutable Form. The golem is immune to any spell or effect that would alter its form.

Magic Resistance. the golem has advantage on saving throws against spells and other magical effects.

Magic Weapons. The golem's weapon attacks are magical.

Sticky Trail. Whenever the golem moves, it leaves a 5 ft. wide trail of wet concrete behind it. Until the start of the golem's next turn, that trail is considered Difficult Terrain, and any creature that tries to pass through the trail must succeed on a DC 15 Strength saving throw or have the Restrained condition until the trail vanishes.

Multiattack. The golem makes two Slam attacks.

Slam. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 16 (2d10+5) bludgeoning damage.

Engulfing Pavement. The golem attempts to envelop a creature with its flowing body by moving into its space. The creature must succeed on a DC 15 Dexterity saving throw or be engulfed. An engulfed creature has a speed of 0, disadvantage on attack rolls, and has total cover against attacks and other effects outside the golem. The creature takes 17 (5d6) acid damage at the start of each of the golem's turns.

The golem can only engulf one creature at a time. If the golem takes 20 damage or more on a single turn from a creature inside or outside of it, the golem must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate the engulfed creature, which falls Prone in a space within 5 ft. of the golem. If the golem dies, a swallowed creature is no longer restrained by it, and can escape from the corpse using 10 ft. of movement, exiting prone.

Fluid Motion (Recharge 6). The golem liquifies its limbs, giving its Slam attacks an additional 10 ft. reach until the start of its next turn.

Sticky Slam. When the golem makes a Slam attack, it can choose to turn that attack into a Sticky Slam. If the target is a creature, it must succeed on a DC 15 Strength saving throw or have the Restrained condition for 1 minute, as the golem's cement splashes around the target. A restrained creature can repeat its saving throw at the end of each of its turns, ending the effect on itself on a success.