Hydreigon

The above description is our old outline of Hydreigon, and it aged pretty well if we do say so ourselves! With good stats, Brutal Swing from the Deino Community Day enables Hydreigon to compete as one of the best Dark-type attackers in the game. Hydreigon's bulk enables it to be as viable as other Shadow Pokemon like Absol and Houndoom, trailing only slightly behind them in DPS, but lasting much longer before fainting. Drop an Elite TM on Hydreigon if you don't already have this monster prepared to go to battle, it's definitely worth it! 

Best PvE Offensive Moveset

• Bite and Dragon Breath have identical stats and both benefit from STAB, though the former will be the move of choice most of the time as Hydreigon is far stronger as a Dark Type attacker than a Dragon Type attacker.
• Brutal Swing* is limited in accessibility, but it enables Hydreigon to deal huge Dark Type damage.
• Dark Pulse is a major downgrade for Dark-type performance. 
• Dragon Pulse is trails narrowly behind in performance, though its slower damage window risks Hydreigon fainting before its damage can be applied. 
• Flash Cannon doesn't have any use for offense. 

Best PvE Defensive Moveset

• Dragon Breath is slightly more favorable than Bite on defense due to fewer resistances.
• Brutal Swing can be used frequently as a 3-bar move, making it more preferable for defense. 
• Dark Pulse is an inferior option for defense. 
• Dragon Pulse hits slightly harder on defense, but is much easier to dodge. 
• Flash Cannon as a 1-bar move is less likely to be used before Hydreigon faints. 

Dragon Breath and Bite both hit hard with STAB, though the former has significantly better energy gains which makes it the superior choice. 

Brutal Swing is a move limited to Community Day events and Elite TMs, but its lesser energy cost improves Hydreigon's performance and consistency in terms of damage output and shield pressure. Dark Pulse costs noticeably more energy, and it is generally recommended to postpone evolving Zweilous until future Community Day recap events in order to obtain Brutal Swing instead. Dragon Pulse isn't as necessary mainly due to requiring more energy, though it can threaten OHKOs against opposing Dragon-types. Flash Cannon is Hydreigon's only hope at threatening Fairy-type targets in some way, but its expensive cost makes it extremely unreliable.