Unusual Nature. The death’s head doesn’t require air, food, drink, or sleep.

Restrained. Because the Deaths Head is stuck on a spike, attack rolls against the creature have advantage, attacks by the creature have disadvantage (accounted for in the Bite attack) and Dexterity saving throws are made at disadvantage.

Magical mouth. The Death's Head's bites are magical for the purposes of overcoming resistance / immunity to non-magical damage.

Mind-Bending Bite . Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) piercing damage plus 10 (3d6) necrotic damage, and the target must succeed on a DC 12 Intelligence saving throw or it can’t take a reaction until the end of its next turn. Moreover, on its next turn, the target must choose whether it gets a move, an action, or a bonus action; it gets only one of the three.