A speed Deoxys that's level 100 with 31 IVs, 252 EVs, +6 stages, and tailwind has 3672 speed.
Deoxys, in its Speed Forme, is the fastest pokémon with a base stat of 180. In second is Ninjask with a base stat of 160.
3. Pheromosa with 151.
If it’s restricted to the Galar Dex, then the fastest Pokémon is Ninjask, at 160 base speed.