How to Build a Boss Fight With a Custom Boss Bar

Creating the Boss

Spawn the mob you want to use as a boss with Mob Spawner, or form a group with Mob Army if the boss should be multiple mobs. Gear it up with Mob Equip and adjust its armor with Armor Editor so it survives long enough to matter. Apply buffs with Effect Giver to make the fight harder, or use Effect Remover to strip effects you do not want.

Adding the Boss Bar

Place Boss Bar Adder and configure it to display a boss bar for your chosen mob. This gives the fight a visible health bar at the top of the screen, tied to the mob you spawned. Set it up after the boss mob exists so the bar tracks the correct entity.

Running the Encounter

Use Mob Enrager to make the boss hostile and start the fight, or Mob Enrager (Multi) if the encounter involves several mobs at once. Keep the boss alive during testing with Mob Healer, and use Mob Killer to end the fight or clear the arena. Use Perimeter Tool to mark the arena boundary so players stay in the boss room. For a mounted boss, apply Mob Mount so the boss enters combat riding a mount.