Debris Form.
The Broken King is not one cohesive creature, but a scattered mess of animated stone and memory. When reduced to half HP, it loses 5 ft. of movement and its melee attacks become less accurate (−1 to hit), as it struggles to hold its form.

Forgotten Momentum.
If the Broken King moves 10 ft. in a straight line before attacking, it gains advantage on its next melee attack roll. It may use this once per round.

Shardfall (Recharge 5–6).
The Broken King stumbles and explodes outward, sending shards of statue in a 10-foot cone.
All creatures in the area must make a DC 12 Dexterity saving throw or take 1d4 piercing damage and be knocked prone.