It is Escavalier with a base 20 speed. It learns Metal Burst by level up at level 52. That is for all generations. Outside of Sword and Shield, there is Wormadam Trash Cloak with 36 speed and Bastiodon with 30 speed. However, Escavalier is now tied with Mega Sableye at 20 speed. For not fully evolved Pokémon, there is Shieldon with 30 speed and Rhyhorn with 25 speed (Rhyhorn learns via breeding). All the other Pokémon learn by level up.