Defensive Zygarde-C is a premier wall in AG thanks to its ability to check the majority of physical attackers, including Primal Groudon, Ho-Oh, Necrozma-DM, Dragon Dance Mega Rayquaza, and Zacian-C lacking Play Rough. Rest is important to keep Zygarde-C healthy and remove status ailments such as Toxic poison from Ho-Oh, Primal Groudon, and Necrozma-DM. An anti-setup move is mandatory in order to check sweepers like Dragon Dance Necrozma-DM properly. Haze lets Zygarde-C check opposing Zygarde-C with Dragon Tail, avoid being setup fodder for special attackers like Geomancy Xerneas, and deal with Baton Pass strategies. Alternatively, Coil makes Zygarde-C more threatening offensively thanks to the Attack boosts it provides, but it makes this set setup fodder for opposing Dragon Dance Zygarde-C. Glare is a good option to cripple sweepers like Dragon Dance Necrozma-DM and annoy offensive checks like Xerneas and Primal Kyogre, preventing them from switching in freely.
Mandatory on teams lacking Primal Groudon, M-Ray and Dusk Mane counter.
- Primal Groudon now has the highest usage this month, so a solid wall to it is mandatory. Primal Groudon now runs Jolly nature sets the highest with an usage of 11%, and special sets are very rare.
- Hidden Power [Ice] has seen some usage of 10%, but it doesn't matter since Zygarde-C without special investment takes only 50% from Hidden Power [Ice].
- Mega-Rayquaza's solid wall, but precaution should be taken against the very rare Draco Meteor which has seen 23% usage though.
- Completely walls Dusk Mane and has counters for its every tactic. Glare stops Dragon Dance while Haze/Dragon Tail can phaze it comfortably. Also it gets Rest for countering Toxic of Ho-Oh, Eternatus and DM.
It can also check Zacian-C to some extent, due to it getting lower usage stats and Play Rough has seen lower usage stats, i.e. 58% compared to 80% Close Combat and 60% usage.
Gets Coil, which is simply a-m-a-z-i-n-g, since Play Rough deals only 30% to complete forme at +1 Defense.
As such, it is ranked +A in the National Dex AG viability rankings, and it should be even used more, like mandatory on a team due to Primal Groudon being the most used Pokemon in the tier.
Hope this helps.