Regulation M-B's conversation has been dominated by Mega Evolutions, but three non-Mega additions deserve serious attention: Gholdengo, Annihilape, and Grimmsnarl. Each brings an ability or stat profile that reshapes how teams are built around it.
Gholdengo is the most strategically disruptive of the three. Its ability, Good as Gold, makes Gholdengo completely immune to all status moves — Spore, Will-O-Wisp, Taunt, Thunder Wave, and every other status targeting move simply fail against it. In a format where Spore and Will-O-Wisp were reliable ways to take opposing Pokémon out of the game, a switch-in that categorically ignores them forces teams to use direct attacking moves to remove it. Gholdengo also has strong offensive stats and a Steel/Ghost typing with few weaknesses, making it difficult to remove even if your opponent knows what it does.
Annihilape brings Rage Fist — a Ghost-type move that increases in base power every time Annihilape takes a hit. A Pokémon that gets stronger the more damage it receives is a natural fit in formats with spread damage and multi-target moves. Its Normal/Ghost dual typing means it has exactly zero weaknesses that hit it conventionally: Normal moves don't affect Ghost types, Ghost moves don't affect Normal types. The only reliable ways through are Dark and other Ghost moves.
Grimmsnarl is a utility support pick. Prankster gives its non-damaging moves priority, meaning Thunder Wave, Light Screen, and Reflect go before almost everything else on the field. Grimmsnarl with Light Clay and Prankster becomes one of the fastest screen setters in the format, and it does it without needing Tailwind or dedicated speed control.
None of these three will top a tier list, but each of them quietly warps how opposing teams have to play. Check their full entries in the Pokémon database.