Tunneler. The umber hulk can burrow through solid rock at half its Burrow Speed and leaves a 10-foot-diameter tunnel in its wake.
Multiattack. The umber hulk makes three Rend attacks.
Rend. Melee Attack Roll: +8, reach 10 ft. Hit: 12 (2d6 + 5) Slashing damage.
Confusing Gaze (Recharge 5–6). Wisdom Saving Throw: DC 14, each creature in a 30-foot Cone. Failure: The target can't take Reactions until the start of the umber hulk's next turn, and the target rolls 1d8 to determine what it does on its next turn:
1-4. The target does nothing.
5-6. The target takes no action or Bonus Action and uses all its movement to move in a random direction.
7-8. The target makes a melee attack against a random creature within its reach or does nothing if it can't make such an attack.