Bloodseeker is not the most resistant hero to melee attacks, but he is surely one of the best when it comes to spells. He is not even a fast hero, so why is he so popular? He is one of the fewest melee agility heroes, making him great in close combat because of his powers.
With his Bloodrage, he increases the attack damage, and he can cast this spell on himself. Even if he is not a fast hero generally, his speed grows incredibly when he sees blood and dying enemies. He can also cast Blood Rite, a spell that damages enemies in a certain area. His ultimate, Rupture causes life force trail if they dare to flee from the battle.