Zygarde @ Lagging Tail
Ability: Prankster / Triage
EVs: 4HP/ 252 Def / 252 SpD
Sassy or Relaxed Nature (+SpD, -Spe) or (+Def, -Spe)
IVs: 0 Spe
- Metal Burst
- Dig / Thousand Arrows
- Copycat / Taunt / Aromatherapy / Drain Punch
- Shore Up
Take some hits, hit them back harder regardless of the type of the user, as Metal Burst is Steel - meaning it has no Type Immunities, and hits foes at 150% of the damage they dealt to Zygarde, regardless of whether the move is a Physical or Special Attack.
Lagging Tail means moves in the same speed priority bracket as the foe always go last, which ensures Metal Burst is used after the foe, since it has 0 priority (unlike Mirror Coat and Counter), while also allowing Dig and Copycat to take advantage of Prankster, to get free turns of invulnerability from going first with Copycat but attacking last on the second turn due to Lagging Tail.
If you want real coverage, you can also opt for STAB Thousand Arrows backed by Taunt to force the foe to either switch out or attack and get hit by Metal Burst.
Aromatherapy can be chosen instead to heal off status for itself and the team, since Zygarde is likely to stick around for a while.
Pokémon with Soundproof can avoid Metal Burst, and Yvetyl counters Dig+Copycat, as it is immune to Prankster due to it being a Dark type, but still gets hit by Metal Burst on whatever attacks it uses.
Shore Up is used for recovery since Sandstream Pokémon are occasionally used, and Zygarde is immune to Sandstorm.
Zygarde is chosen for having high HP, decent defenses without an item (Eviolite Chansey fears Knock-off / Trick), and STAB off of an invulnerable move or its coverage equivalent in Thousand Arrows.
Zygarde has a +SpD nature first because it is more likely to be hit by Ice Beam than Ice Hammer or Icicle Crash, and will need to survive the hit in order to Metal Burst.
*Triage can also be used if you plan on having Thousand Arrows paired with Drain Punch and works great on hitting Ice-Types on the switch-in such as Weavile, Kyurem-Black, or Kyurem-White that think they can force it out with Refridgerate sets.
Drain Punch works great on Dark Types that think because your Shore Up has priority it must be a Prankster set, only to get a Super Effective Fighting Type move to the face.