They're 3 different bosses so far in esper online, wich are the followings, the bosses have much more hp then any regular mobs and does high damage and unlike other mobs that the player may encounter the bosses/mini-boss have special abilities that can easily kill the player. The bosses are the following:
-Teru, The Pyromancer (Mini-Boss)
-Warlow, The ghost knight (Boss)
-Glacius, Guardian of The Ice Palace (Boss)
Teru, The Pyromancer
General Info
Teru is the first mini-boss that the player will encounter in their journey to become the strongest esper that has ever lived
Teru has a decent amounts of hp and run slowers then the player's sprinting movement speed, but can deal aoe damage using his special ability, as fearsome as he may look Teru only has 2 abilities
Abilities
-Basic punching combos (Does around 400 damages per punch and stuns you for a short moment after each punch)
-Fire explosion (Teru stops chasing the player and cross his arm, shortly after doing that Teru release a fiery explosion that surronds him for a couple of meters, deals around 440 damages and burns the player for an extra 50 damages)
Reward
Killing Teru has a 10% chance of dropping a Fire Orb wich can be picked up to complete the quest that Reigen gives to the player
Warlow, The Ghost Knight
General Info
Warlow is going to be the first real boss that player will fight and posses a much bigger challenge then Teru, dealing much more damage and more abilities
Warlow has much more hp then Teru and can teleports after players making it impossible to safe-spot
Abilities
-Standard Punch (Deals 2,000-4,000 damage)
-Teleportation (Teleports towards the current agroed player then immediately punches the player)
-Spin Attack (Worlow spins his body and generate a huge whirlwind that damages all players in a medium radius for 4000-5000 damage)
Rewards
Killing Warlow will always drop a Green Crystal that can be picked up for 5,000 Yen and 100,000 xp
Glacius, Guardian of The Ice Palace
General Info
Glacius is the last boss that the player will encounter in it's journey (so far) and by far is the strongest enemy in the game
Glacius, just like Worlow can teleport but can also uses multiple long-range and close-range abilities
Abilities
-Ice Bomb (Glacius launches an ice orb at the player, the orb will explode on contact and freeze the player along with dealing alot of damage)
-Blizzard Wind (Glacius slam his fists on the ground and creat an icy windy explosion that deal very high damage and freeze the player
-Teleportation (Glacius teleports to the agroed player and punch the player right after Glacius teleports)
-Fists Slam (Glacius slam his fists on the player dealing medium damage)
Rewards
Killing Glacius will always drop an Ice Orb that can be picked up only if the Killing Glacius quest is active, picking the Ice Orb will complete the quest yielding 525,000 xp and 10,000 yen