Boneskull

Shattering Defense. Every time a creature makes an attack against the boneskull, Miss or hit, it loses 1 AC. (Goes back to 18 at the end of every battle.) When the boneskull has 10 AC or lower at the beginning of it's turn, it becomes enraged and does critical hits every time it attacks until it dies. Every attack against it while it is enraged has advantage, and it is vulnerable to all types of attacks.

Terrible Agility. The boneskull gets disadvantage to all Dexterity based rolls.

Fortify. The Boneskull spends it's turn to fortify it's defense, and get ready to charge. It gains +2 permanent AC and it's next attack has advantage.

Headbutt. Melee Attack: +3 to hit, reach 20 ft., 1 target. Hit: 9 (2d6 +2 ) [Bludgeoning] damage. Charges forward 15 feet to Headbutt. It does not have to charge all the way but if it charges a full 15 feet than it gets an extra d6 damage on it's attack.

Slam. Melee Attack: +6 to hit, reach 5 ft., up to 8 targets. Hit: 3 (1d4 + 1) [Bludgeoning] damage. Hits everyone adjacent to the Boneskull. (Friendly Fire) And every creature that gets hit gets moved back 20 feet, and must make a (DC 12 + the amount of damage that was dealt to it by this attack) Constitution saving throw or be knocked prone, and takes an extra 1d6 damage. If it hits at least four people, it may immediately take the Headbutt action.

As a bonus action, boneskulls can choose to make a way powerful attack. This provides a -5 to hit, but if it does hit, it gives an extra d8 damage to any attack. This has a 2 TURN COOLDOWN. The boneskull can only use this every three rounds.

Boneskulls have no reactions.

A boneskull has no Legendary actions.

A boneskull has no Mythic actions.