PaniK, known as the Player Killer of Darkness in the manga and Japanese anime, and known as Yamitsukai in certain video games, is a player eliminator hired by Maximillion Pegasus. He is a brutal man who targeted Duelists who had earned many Star Chips. When Yugi Muto and his group arrive, Mai has just been defeated by him.
In order to salvage the situation and return Mai's Star Chips, Yami Yugi challenges PaniK to a Duel. Upon losing, PaniK then activates the flame ejectors that are in the ring, attempting to incinerate Yami Yugi. However, Yami Yugi is safe because of the power of the Millennium Puzzle, and he inflicts a Mind Crush on PaniK.
In the English anime, PaniK's soul is sent to the Shadow Realm. In the Japanese anime, Yami Yugi "purifies his evil heart" by inflicting a Mind Crush on him. In the manga, PaniK was given a Penalty Game that gives him the illusion of being hanged; he ended up screaming nonstop at the illusion as Dark Yugi took all the Star Chips and left the Battle Box.
Because of his brutality and the apparent frequency with which he knocks Duelists out of the tournament, he wears 2 double-sized Dueling Gauntlets. This may likely reference his role as a Player Killer as well; during their duel in the manga, Yami Yugi pondered if PaniK's role was to eliminate 10 of the 21 finalists; indeed, PaniK forced Mai to wager all eight of her Star Chips in their duel despite she only needed to wager two to achieve the ten required. In the manga, instead of flamethrowers, PaniK has a cord from the glove that he uses to bind the opponents by their neck to prevent escape, and to strangle them if he gets angry. Yugi, betting his life in lieu of the two extra Star Chips that he tried to retrieve for Mai, had the cord around his neck, and PaniK planned to use it to choke him twice if he wins.
PaniK also appeared in the Waking the Dragons arc as one of the lost souls wandering the sacred circle Yami Yugi ventures through to find his other half.
Panik plays a "Darkness" Deck. Using "Castle of Dark Illusions" he conceals his monsters within a field of shadows, protecting against attacks since his opponents cannot see his cards and thus cannot know how powerful they are; the Night also provides his monsters with a Field Power Bonus, while covering other terrains, preventing his opponents from gaining the same advantages.
His monsters are Fiend-Types with unusual ATK and DEF values, ending in 10, 30, 80, etc, while most monsters have values that end in 00 or 50. This is so that their ATK and DEF become close to their manga ATK and DEF after they gain the Field Power Bonus from the night. e.g. "Castle of Dark Illusions" had 1200 ATK and 2500 DEF in the manga. In the anime it had 920 ATK and 1930 DEF, which rose to 1196 and 2509 after the Field Power Bonus. In the manga, it did not gain a Field Power Bonus.
When his monsters are revealed by "Swords of Revealing Light", Panik switches to a defensive strategy, bolstering his monster's DEF with "Chaos Shield". Yami Yugi claims Panik's method of Dueling is the way of a coward, only powerful when he strikes from the shadows and cowering when confronted in the open, with Yugi's counter-strategy using Panik's reliance on defense against him by putting him in a position where his defenses trap and destroy his own monsters.