Cavern Crawler

Tunneler. The Cavern Crawler can burrow through solid rock at half its burrow speed and leaves a 5-foot-diameter tunnel in its wake.

Multiattack. The Cavern Crawler makes two attacks: one with its bite and one with its claws.

Bite. Melee Weapon Attack: +1 to hit, reach 5 ft., one target. Hit: 6 (2d4 + 1) slashing damage.

Claws. Melee Weapon Attack: +1 to hit, reach 5 ft., one target. Hit: 6 (2d4 + 1) slashing damage.

Surprise Attack. If the Cavern Crawler burrows at least 15 feet as part of its movement, it can then use this action to resurface in a space that contains another creature of an equal or lesser size. Each of those creatures must succeed on a DC 8 Dexterity saving throw or be knocked prone and take 6 (2d4 + 1) slashing damage. On a successful save, the creature takes no damage, isn't knocked prone, and moves 5 feet out of the Cavern Crawler's space into an unoccupied space of the creature's choice. If no unoccupied space is within range, this attack proceeds as normal. If the targeted creature is larger than the Cavern Crawler, the creature is completely unaffected, and the Cavern Crawler takes 2 bludgeoning damage and must move 5 feet out of the creature's space.