Giygas, while he can work as a playable character, at least in his appearance in the original Mother game, would perfect as a boss in either of his appearances, and I hope to see him as such. I'd love to fight him twice in a level on Mt. Itoi and then later in the Cave of the Past.
I'd rather have Porky Flint & Boney, Jeff, or Masked Man as the third Mother rep, and if we get one, it's probably going to be Porky since he's now more well-known because of EarthBound on the VC, and evens out the playable Mother 2 and Mother 3 representation, being an enemy of Ness AND Lucas, and Sakurai definitely knows of his importance since he had a level, boss battle, stage, and have course a trophy dedicated to him.