A Very Manta Christmas
Written as a humorous side-story several years ago (and never finished), the Manta christmas episode took place during one of Manta's numerous stop-offs in his time-travelling journey toward his arrival in the modern era. In it, Manta arrives at some undisclosed time period in the Mana Dimension, being deposited just off the coast of the Ice Country. There, he is discovered by the Todos, who hire him to assassinate their ruthless master, Santa Claus, who turns out to possibly have severe bipolar disorder and flies into uncontrollable manic rages.
The story, as stated, was never finished, but clearly Manta emerged victorious from the fight with Santa Claus himself.