Bloodied Condition

Once a creature reaches half of its maximum hit points (rounded down), the creature has the bloodied condition. Bloodied is a visual condition that gives the players an indication of how hurt a creature is in battle. If an attack from a player causes the bloodied condition, the DM will describe how that attack results in the creature being bloodied. A creature that has recharge abilities regains those abilities once they are bloodied.
Some features, abilities and attacks that can only be used when a creature has the bloodied condition (or only against bloodied creatures) can be added to monsters to add more depth to combat.