The Doom Knight card is a card played by Jaris Varlen.
This card was only played in Jaris' duel against Yami Bakura. The duel was to decide which of the two would gain total control over the parody series created by Jaris, and was sparked by Yami Bakura's indignance over how he was portrayed.
This card was on the field when Jaris lost. He was about to Tribute a Necrosoldier he had Summoned back from Bakura's Graveyard to destroy Bakura's Life Points and win the duel, but Bakura activated Fissure to destroy it, even before it could multiply. When his Doom Knight finally declared its attack, Bakura activated Jaris' only weakness:
Magic (Friggin') Cylinder. Bakura won, because Jaris had only 2500 Life Points left.
TYPE: Warrior / Evil / Effect
-Once per turn, if you take Battle Damage, the same amount may be inflicted upon your opponent's Life Points as Battle Damage.
-If this monster was Summoned by the effect of a "Corruption Soul," once per turn, you may Tribute one monster you control to inflict 1000 damage to your opponent's Life Points. However, if this effect is activated, the controller takes 500 points of Effect Damage.