Crystal Flesh Mound

Berserk. Whenever the mound starts its turn with 40 hit points or fewer, roll a 1d6. On a 6, the mound goes berserk. On each of its turns while berserk, the golem attacks the nearest creature it can see. If no creature is near enough to move to and attack, the golem attacks an object, with preference for an object smaller than itself. Once the golem goes berserk, it continues to do so until it is destroyed or regains all its hit points.

Aversion of Fire. If the mound takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.

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

Lightning Absorption. Whenever the mound is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt.

Magic Resistance. The mound has advantage on saving throws against spells and other magical effects.

Magic Crystals. The mound's weapon attacks are magical.

Crystal Ooze. The mound takes up its entire space. Other creatures can enter the space, but a creature that does so is subjected to the mound'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 mound. Doing so requires a successful DC 12 Strength check, and the creature making the attempt takes 3d6 acid damage.

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

Multiattack. The mound makes two slam attacks.

Slam. Melee Weapon Attack: 1d20+7 reach 5 ft., one target. Hit: 2d8 + 4 bludgeoning damage.

Pseudopod. Melee Weapon Attack: 1d20+7, reach 5 ft., one creature. Hit: 10 3d6 acid damage.

Engulf. The mound moves up to its speed. While doing so, it can enter Large or smaller creatures' spaces. Whenever the mound enters a creature's space, the creature must make a DC 12 Dexterity saving throw.

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

On a failed save, the mound enters the creature's space, and the creature takes 3d6 acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 6d6 acid damage at the start of each of the cube's turns. When the mound moves, the engulfed creature moves with it.

An engulfed creature can try to escape by taking an action to make a DC 12 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of the mound.

Crystalisation: The mound spreads a blood crystal spore onto the attacker, at the beginning of every turn, the attacker has to take 4d4 piercing damage