Swords'n Shields, Aegis should be 1st lmao, but since it's too late: Aegislash was one of the most dangerous pokemon on the tier, He not only could pressure a big portion of the metagame, he was also unpredictable, It was hard to wear down since he was immune to Toxic, Resisted rock, 3 Immunities, A bunch of resistances, Great movepool on both Phys. and Sp. sides, it was so easy to set up Subs or SD, had STAB priority and the most important: Kings Shields, with that he could come back to its amazing 60 / 150 / 150 bulk and halve  the opponent's attack, reducing its possible checkers to a minimum level. Behind subs, he was the scariest thing possible in the metagame, since most of its checkers were reduced to at least Soft-Checker status. After a SD, It could hit almost everything thanks to its Priority Ghost / Steel / Fighting coverage. But he was far beyond for being limited by these sets, He could be a speedy special attacker, Defensive, Sp.Defensive, SubToxic, Mixed AoA and Lead. He is definitely the best non-legendary or mega Kalos pokemon.