The Mother of Golden Pigs is the final boss of the Golden Cloud Castle, a bonus dungeon exclusive to "portal-campaign" events. Upon defeat, this pig will drop 10 Lucky coins, and a small amount of Snoutlings and Xp.
Because of the pig's lucky coin reward, this pig makes fighting the GC Castle over the daily dungeons (and using up their free play with Piggy McCool as a result) worth it.