Megasparce appears three times in-game as a Pokemon used by Elite Four member Wilson and is one of the so-called "Six Kings" of his team used in the Hall of Masters. Not much is known about Megasparce aside from the fact that it was synthetically created, as described by Sir_Willis_CMS in the data given from a "secret laboratory file":
LOAD DATA ON: MEGASPARCE DATA LOADED MEGASPARCE, THE NIGHTMARE DRAGON. FIRST KING, HIGHLY ADAPTABLE CREATED FROM THE DNA OF DARKRAI, ZEKROM, AND DUNSPARCE DATA END
Because Megasparce cannot be obtained by the player, it is not possible to obtain a full list of the moves it is capable of learning. However, there are a few moves that are known from the player's battles with Wilson. Additionally, Wilson's Megasparce always has Devour occupying its move list twice, effectively meaning it only has 3 moves to use during each battle.