Bladesoul

Bladesoul is a that spawns in the  area in a small, circular arena to the right of the Crimson Isle entrance.

Spawning
Bladesoul spawns around 5 minutes after being defeated at -295 83 -518

Drops
Bladesoul drops Hallowed Skull which is needed to complete one of the Dean quests.

Behavior
Bladesoul will attack one player at a time using its Ragnarock Axe. Occasionally, it will shoot one or more wither skulls that deal a high amount of damage.

At some point in the fight, Bladesoul may summon a Wither Guard, a mob the height of a baby zombie with

Whenever Bladesoul attacks, the Wither effect is inflicted.

Trivia

 * The Bladesoul's lore states that the blaze on its head is the corpse of one of its enemies that the Bladesoul defeated: A giant wither skeleton who rules over the stronghold after defeating the strongest of the Blazes in it, now wearing his body as a crown.