Someone should really tell Game Freak that remoras (those little fish you often find attached to larger fish such as sharks) do not turn into octopuses. They're distinct species that have little to do with each other. But for some reason, Game Freak decided that Remoraid should evolve into Octillery and start shooting things out of its beak.
Pokémon are weird. Here's where you can find a Remoraid and how to evolve it into Octillery in Sword & Shield.
Where To Find Remoraid & Octillery
Both Remoraid and Octillery can only be found in bodies of water, so have your fishing rod handy. Remoraid is in Route 9, South Lake Miloch, West, and Lake Axewell, while Octillery is in Route 9, Axew's Eye, and South Lake Miloch. You can find both in Max Raid Battles at East Lake Axewell, North Lake Miloch, South Lake Miloch, West Lake Axewell.
As with most Water-types, Remoraid and Octillery are more commonly found when its raining or during thunderstorms.
How To Evolve Remoraid Into Octillery
Remoraid becomes Octillery after it reaches level 25.
What Octillery Can Do In Battle
Octillery can have the Sniper ability, which makes all critical hits extremely potent. For this reason, Focus Energy can be a good move to use if you can keep Octillery safe for a turn.
Otherwise, strong STAB moves like Hydro Pump and Water Spout are good ideas, along with good coverage moves like Energy Ball and Ice Beam.