Bosses appear when you enter their arena. Their health bar shows on top.
At 66 % and 33 % they change phase: minions, rage. More players = more health (up to +100 %).
Flee and they retreat after 60 s – and return healed.
Abilities: shockwave, arrow volley, fireballs, fire ring, teleport, frost, poison clouds, levitation bullets, fangs, sandstorm, web, roar, curse.
Defeated: lots of XP, loot, a 50 % chance for a relic – and the treasure chest opens. The boss returns after 3 hours.