Zygarde @ Groundium Z / Leftovers  
Ability: Power Construct  
EVs: 12 HP / 252 Atk / 244 Spe  
Adamant Nature  
- Substitute  
- Shore Up  
- Dragon Dance  
- Thousand Arrows
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Optional Move(s):
- Dragon Tail
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Zygarde @ Leftovers  
Ability: Power Construct  
EVs: 252 HP / 252 Def / 4 SpD  
Impish Nature  
- Shore Up  
- Thousand Arrows  
- Dragon Tail  
- Toxic / Coil
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Optional Move(s):
- Glare
- Spikes
- Haze
Optional EV/IV(s):
- 4 HP / 252 Def / 252 SpD  Impish Nature
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Overview:
Zygarde's Power Construct ability grants it a gigantic HP stat that makes it much easier to set-up or reliably check the majority of physical attackers after dropping its HP to half or below. Its naturally access to Thousand Arrows dents any Ground-immune Pokemon and allows it to have a free moveslot to choose other moves. It is worth noting that most of its greatest traits are only occured when it activates its Power Construct safely, its base form suffers from lack of bulk if not invested and high vulnerability to Fairy and Ice attacks, which could lead to being overwhelmed by strong offensive pressure. Its average Attack stat and 90 Base Power from Thousand Arrows makes Zygarde passive on defensive set and often needs to set-up multiple times in order to deal heavy damage on offensive set, notably sets who lack heavy Attack investments. It is also vulnerable to status moves such as Toxic and Will-o-wisp on sets lacking Substitute.