I've got a bunch of suggestions here. A few of these may be pushing the limits of viablility, but I've included them since this list is more for possible roles rather than viable roles. Some of these have already been mentioned, but I agree with the suggestions so I'll restate them.
Toxic Spikes: Forretress
Hazard Control: Mega Aerodactyl
Wish/Healing Wish: Mega Audino
Heal Bell/Aromatherapy: Diancie, Mega Audino
Walls:
Mixed: Mega Audino (it could probably fit in any wall category to be honest)
Pivots:
Defensive: Vaporeon
Fire Checks: Snorlax, Slowking
Dark Checks/Knock Off Switch-ins: Mega Audino
Water Checks: Cacturne, Serperior, Amoonguss
Volt Switch-ins: Flygon, Gastrodon
Stallbreakers/Wallbreakers: Reuniclus, Sigilyph, Krookodile (does Taunt Krookodile count as a stallbreaker?)
Choice Users:
Scarf: Azelf, Shaymin
Band: Machamp, Stoutland, Pangoro, Escavalier, Arcanine
Specs: Exploud, Magneton, Espeon
Setup Sweepers:
Swords Dance: Shedinja
Calm Mind: Mega Audino, Cofagrigus
Nasty Plot: Azelf
Dragon Dance: Scrafty
Shell Smash: Gorebyss
Bulk Up: Scrafty
Curse: Snorlax, Quagsire, Mega Steelix, Umbreon
Focus Energy: Kingdra (Critda's a setup sweeper, right?)
Phazers: Empoleon, Suicune, Mega Steelix, Milotic, Goodra, Dragalge (Dragon Tail is phazing too)
Priority Users: Donphan, Spiritomb