Manawyddan fab Llyr is the Yu-Gi-Oh! The Duelists of the Roses incarnation of DarkNite and portrayal of the Welsh mythological figure Manawydan, son of Llyr. He serves as the antagonist of the game and is the only opponent the player will face irrespective of which team they side with, Red or White Roses.
He will imply that he is Nitemare's brother when summoned if the player chose to follow the Yorkists, by saying "First you humans awakened my brother from the sands of Egypt and sealed him away again!"
Manawyddan fab Llyr uses two Decks with two different Deck leaders. The player faces the "Skull Knight" version if they chose to side with the Red Roses and the "Chakra" version if they side with the White Roses.
The Chakra Deck uses mainly monster cards with ATK points of 2400 or more and the Skull Knight one is primarily Magic and Trap cards that inflict damage.