Hey, recently I've been testing Shaymin and I think that, not only is it viable enough in CAP to be added to this list, it is growing in popularity.
Shaymin is a great Water check, owing to it's Grass typing and Seed Flare.
Also, Life Orb Shaymin is great as a wallbreaker. Assuming a set with Seed Flare, Earth Power/Dazzling Gleam, and Psychic, it 2HKOes Assault Vest Colossoil, Cyclohm, Fidgit, Naviathan, Tomohawk Clefable, Garchomp, Specially Defensive Gliscor, Hoopa Unbound, Defensive Landorus, Mega Sableye, and Tyranitar. It OHKOes Krilowatt, non-Assault Vest Azumarill, non-Special Wall Hippowdon, Rotom-Wash, and Slowbro. Seed Flare's 40% chance of lowering the opponent's Special Defense by 2 stages is also very nice.
The above reasoning can probably also apply to placing Shaymin as a stallbreaker.