Shadow Empoleon

Empoleon has always been a bit of an underdog Water Type, and its Shadow forme is no different. While genuinely strong, it's not the best Water Type attacker, standing in the shadow of many other Water Types that leave it in the dust. Part of that fact is due to the fact that its Steel sub-typing generally does it no favors, as it loses its resistance to Fire while also gaining a weakness to Ground. However, it is useful against Rock Type movesets, and isn't THE WORST Pokemon to raise if you need Water damage.

Best PvE Offensive Moveset

• Waterfall and Hydro Cannon* make Shadow Empoleon a viable Water-type attacker. Hydro Pump is an unexciting replacement to the Community Day exclusive move and is noticeably weaker.

• Metal Claw with Flash Cannon counters Fairy-types, but it’s underwhelming.

• Metal Claw + Hydro Cannon provides a combination slightly better against Rock-type Pokemon.

• Even without STAB, Blizzard is generally superior to Flash Cannon.

• Drill Peck lacks STAB and has no use. 

Best PvE Defensive Moveset

• Waterfall out-paces both Steel Wing and Metal Claw on defense.

• Hydro Cannon is an optimal choice for damaging attackers.

• Drill Peck can be spammed frequently as a 3-bar move, and is also great against Fighting-type attackers. 

• Hydro Pump is stronger than Flash Cannon; both can be hard to dodge.

• Blizzard probably won't get a chance to launch, but it can severely maim many common gym cleaners like the big-name Dragons.
• 
  

Steel Wing offers the best overall combination of damage and energy, making it the preferred option. Waterfall can be used to further lean in on Empoleon's Water-type damage. Metal Claw is horrendous.

Hydro Cannon is one of the most powerful charge moves in the game, and is necessary not only for its high DPE value, but also due to its significantly less energy cost. Drill Peck ties for the cheapest charge move energy-wise, which is important as Empoleon's bulk is middling. It also provides useful coverage against its vulnerability to Fighting-type Pokemon. Flash Cannon benefits from STAB and is cheaper than Blizzard, but the latter provides significantly more valuable coverage. Neither of these two moves are recommended due to their expensive energy costs.