This Undead Paladin is called a Gate Knight, a guardian whose soul and body is fused to an enchanted body of armor. He is able to sacrifice his left arm (Key Gauntlet) to open a portal to the underworld.
One cut from his broad blade, Sender, is all it takes to brand his opponent for the underworld. The blade leaves a branding that triggers a thousand clawed hands appear to drag the soul to the underworld.
The Gate Knight is extremely strong, wielding the 2 handed blade like a one handed sword. He’s incredibly fast for one who is dead, and he barely feels pain and doesn’t need to breath.. The only downfall is when the portal is open his body is linked to it (left arm creates spiritual connection). This limits him in how far he can travel from the portal. It also limits him on defense, for he can only use his right arm to wield a weapon.