The Dreadknight is a post-Helvius boss. Progression Map Page: Post-Helvius
The Dreadknight can be summoned at a Summoning Station using Guardian's Flesh as the ignition.
The Dreadknight has a total of 20 health. Though this number may seem small, the Dreadknight wields an extremely powerful armor set called the Bloodsteel Set, including the Dread Blade. The Dreadknight has a follow range of 500, a movement speed of 0.3, and cannot drown.
The Dreadknight behaves exactly like a zombie would, dashing at you if in Master/Grandmaster Mode. When the Dreadknight is between 1 and 7 health, the Dreadknight will rise up 20 blocks and summon a very harmful area effect cloud called Dreadrage that will leave you at half a heart regardless of armor if you don't escape the attack in time. Beyond this point, you will be blinded for the rest of the fight. The Dreadknight will despawn if there are no players present.
Upon killing the Dreadknight, you will receive The Dread Blade and the full Bloodsteel armor set.