Colossal Skeleton

Multiattack. The skeleton makes three attacks: two with its maul and one kick attack.

Great Maul. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit 28 (6d6 + 4) bludgeoning damage.

Kick. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit 20 (4d6 + 4) bludgeoning damage and the target is pushed 15 feet and knocked prone.

Slow (Recharge 5-6). The skeleton targets one or more creatures it can see within 10 feet of it. Each target must make a DC 17 Wisdom saving throw against this magic. On a failed save, a target can't use reactions, its speed is halved, and it can't make more than one attack on its turn. In addition, the target can take either an action or a bonus action on its turn, not both. These effects last for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Can take a legendary action at the end of another players turn. Having a total pool of 3 to work from. Regenerating an action on the end of his turn.

1. Spawn Skeletons (Costs 1 Action). The Colossal Skeleton points towards the grown and rises Four Skeletons from the earth.

2. Sword Strike (Costs 1 Action). The Colossal Skeleton makes one strike with his arm like a sword  Melee Weapon Attack: +7 to hit, reach 5 ft., one target 2d8 necrotic and 2d6 slashing damage.

3. Lord Call (Costs 3 Action). The Colossal Skeleton makes a loud unearthly scream, calling all bones from the undead in the surrounding area, attaching the bones to himself. Possibly adding additional bonuses such as wings if a dragon large enough was absorbed. He regens 2d8 HP per skeleton.