Zygarde-C possesses titanic bulk, rivaling that of Eviolite Chansey, thanks to its outstanding HP stat and great defensive stats. It also has a great Dragon / Ground defensive typing that allows it to resist many common offensive types such as Fire, Electric, and Rock. This allows Zygarde-C to blanket check many common metagame threats such as Primal Groudon, Mega Tyranitar, and Mega Mewtwo X if they lack Ice coverage. It can run many defensive sets such as Fur Coat, Unaware, and Poison Heal that allows it to fit well on a variety of teams and sometimes makes it mandatory on more balanced builds. Zygarde-C can also run surprise sweeping sets such as Shift Gear Poison Heal and Quiver Dance Soundproof sets that allows it to garner more of an offensive presence. Although offensive Pokemon such as Mega Gengar, Mega Rayquaza, and Mega Mewtwo Y can pull off sweeping sets much better due to their better damage output, they trade off the amazing bulk that Zygarde-C has access to.
However, Zygarde-C has a nasty 4x weakness to Ice that offensive threats can exploit by running appropriate coverage moves to weaken it down immensely with examples being Refrigerate Mega Mewtwo X and Ice Beam Primal Kyogre. This typing also gives it a weakness to Fairy- and Dragon-type attacks, which are also quite prevalent in the current metagame. It is also quite weak without any setup boosts, which means it can be passive at times.
Haze allows Zygarde-C to reset all stat changes on the field, allowing it to check many common setup sweepers such as Mega Mewtwo X, Primal Groudon, and Regigiggas. Thousand Waves is a great STAB move that allows Zygarde-C to trap opposing Pokemon and proceed to stall them. Thousand Arrows is alternative STAB option that can be used if Zygarde-C is running a pivot move. Shore Up is a reliable recovery move that allows Zygarde-C to sustain itself and and be a more consistent wall. Core Enforcer is a STAB option that allows Zygarde-C to prevent common Poison Heal users such as Regigigas, Primal Kyogre, and Arceus from setting up. It also works well with Thousand Waves, as it allows Zygarde-C to trap and stall out Poison Heal Pokemon. U-turn can be used as a pivoting move that allows Zygarde-C to switch out on incoming Pokemon that threaten to hit it hard and provides momentum for your team. Defog is another option that allows Zygarde-C to clear all entry hazards, which may be more beneficial for its teammates.
As Unaware allows Zygarde-C to ignore stat boosts, and Prankster + Haze can remove them before Zygarde-C takes a hit, Zygarde-C is an excellent check to certain setup sweepers, which is invaluable for more defensively orientated teams. Safety Goggles allows Zygarde-C to be immune from the most common form of sleep inducement in Spore, which can help it check certain setup sweepers more easily. Groundium Z makes Zygarde-C immune to Trick, meaning it has a much easier time facing common Trick users such as Primal Groudon. Tectonic Rage can also act as an emergency tool to hit Entrainment Mega Gengar as well. Leftovers is another option on any defensive Pokemon but generally has less utility than the other two items. EVs are maxed out in HP, Attack, Defense, and Special Defense with a Relaxed nature to allow Zygarde-C to become a bulky wall, allowing it to avoid the 2HKO from Choice Band Primal Groudon's Precipice Blades and Psystrike from Mega Mewtwo Y. It also ensures the effects of Core Enforcer activate as much as possible.
When using Unaware, be wary of certain setup sweepers that carry ability-ignoring moves such as Sunsteel Strike and Moongeist Beam, although Zygarde-C can usually avoid the 2HKO from common Sunsteel Strike and Power Trip users, such as Mega Gengar, Mega Rayquaza, Primal Kyogre, Yveltal, and Mega Mewtwo X. Prankster Zygarde does not fear these moves; however, it's important to switch it into Pokemon that you predict will use setup moves so that it will not need to take any boosted hit. Zygarde-C cannot always switch in on certain special setup sweepers such as Mega Mewtwo Y, Mega Rayquaza, and Deoxys-A, as they can sometimes 2HKO Zygarde-C due to its lower Special Defense. Zygarde-C can be worn down quite frequently if the foe has laid down multiple entry hazards, so try and remove them as soon as possible to try and alleviate this issue. It's important to scout for Ice-type coverage from common users such as Mega Mewtwo X, Primal Kyogre, and Primal Groudon when using Zygarde-C, as these coverage moves tend to have the chance to OHKO Zygarde-C. It is also important to keep Zygarde-C at high health due to it having a bit more of a difficult time checking certain threats if it is weakened enough.
Defensive Steel-types such as Solgaleo and Registeel can be great partners for Zygarde-C, as they are able to sustain Ice- and Fairy-type attacks that would otherwise dent Zygarde-C immensely. They also provide a Psychic-type resistance to the team that can help Zygarde-C get passed certain special setup sweepers in Mega Mewtwo Y and Deoxys-A more easily. Pokemon that can check common -ate abilities such as the aforementioned Registeel, Aegislash, and Soundproof Mega Slowbro can help Zygarde-C deal with these wallbreakers without taking a severe amount of damage. Entry hazard removers such as Giratina and Mega Audino can also be quite useful, as they can clear the battlefield from all entry hazards, which grants Zygarde-C a much more easier time when switching in. Specially defensive walls such as Giratina and Primal Kyogre are also useful partners, as they can stomach special attackers such as Mega Mewtwo Y and Kyurem-W.
Core Enforcer is a great STAB option that allows Zygarde-C to punish incoming switch-ins by removing the effect of their abilities. This can be quite useful against certain threats such as Poison Heal Giratina and Poison Heal Primal Kyogre for example. Thousand Arrows is another STAB option that allows Zygarde-C to hit Fairy-types more reliably, but the beneficial side effects from Core Enforcer usually outclass the use of this move. Shore Up acts as an reliable recovery move and allows Zygarde-C to sustain itself and be able to perform its role throughout the match. U-turn allows Zygarde-C to pivot out from incoming Pokemon that would otherwise threaten it out such as Kyurem-B, Mega Rayquaza, and Mega Diancie and allows Zygarde-C to safely bring in teammates due to it being a rather slow pivot. Haze is a useful move that allows Zygarde-C to not be setup bait against certain setup sweepers by nullifying their stat changes, making it a more consistent check to a wider variety of offensive threats such as Power Trip Yveltal and Mega Tyranitar. Metal Burst is another option that can be a useful way of dealing massive amounts of damage thanks to Zygarde-C's amazing HP coupled with its equally high Defense thanks to Fur Coat. This allows it to beat certain physical threats such as Primal Groudon and Mega Mewtwo X more reliably. Although once scouted, the foe can then capitalize on the use of the move by getting free switches.
Fur Coat turns Zygarde-C to undoubtedly the best physically defensive wall in the metagame thanks to its titanic HP stat. EVs are maximized in all stats besides Attack and Speed with a Relaxed nature to maximize Zygarde-C's defensive utility while also ensuring that it provides slow pivoting and also be able to activate the effects of Core Enforcer. Safety Goggles are paired, as it allows Zygarde-C to bypass certain Spore users such as Mega Gengar, Mega Rayquaza, and Deoxys-S. Groundium Z paired with Thousand Arrows can also be used to prevent Zygarde-C from being crippled by Trick Choice items and also can let hit Normalize Mega Gengar even after it has been inflicted with Entrainment. Leftovers is another option that can be used to grant Zygarde-C passive recovery each turn, although Safety Goggles is preferred due to it being more useful in more situations.
Zygarde-C may not be able to switch in on certain physical wallbreakers if they tend to run Ice-type coverage such as Stakeout Primal Groudon and Refrigerate Mega Mewtwo X; however, Zygarde-C can comfortably pivot in on a variety of offensive threats such as Mega Tyranitar, Yveltal, and Regigigas if they do not run Ice-type coverage, and it can then provide your team with useful momentum afterwards. Zygarde-C cannot really switch in to powerful special attacking wallbreakers such as Mega Mewtwo Y, Primal Kyogre, or Deoxys-A all too well, so be cautious of these threats when using Fur Coat Zygarde-C. Certain physical setup sweepers such as Mega Mewtwo X, Yveltal, and Mega Tyranitar sometimes tend to run Sunsteel Strike to bypass their foes' abilities, so be wary of these variants, as they can sometimes OHKO Zygarde-C if boosted enough. Since Fur Coat Zygarde-C possesses immense Defense, it does not always need to be at full health in order to check physical attackers, meaning that it can choose to go for U-turn more often instead of constantly recovering its HP.
Specially defensive walls such as Dialga, Mega Audino, Mega Gyarados, and Registeel complement Zygarde-C well, as they can oftentimes be able to wall powerful special wallbreakers, that would otherwise threaten Zygarde-C. Registeel in particular can be a great partner, as it can resist Sunsteel Strikes from threats such as Kartana and Regigigas. Primal Groudon is also a great partner for Zygarde-C, as it can threaten out many Ice-types such as Kyurem-B and Kyurem-W and can also break through many of Zygarde-C's checks in Dialga, Primal Kyogre (if Desolate Land is up), and Zekrom. Primal Groudon also works very well alongside Zygarde-C, as Zygarde-C can Imposter proof Primal Groudon if it is not running Ice-type coverage. -ate checks such as Registeel, Solgaleo, and Aegislash can also be great partners, as they can deal with certain wallbreakers such as Mega Rayquaza, Mega Diancie, and Kyurem-B that would otherwise threaten Zygarde-C. Powerful Fairy-type wallbreakers such as Mega Diancie and Xerneas can also be good partners, as they can threaten out this Zygarde-C set if the opposing Chansey had transformed into it due to their immunity to Core Enforcer and their ability to hit Zygarde-C extremely hard. Hazard removers such as Registeel and Mega Audino are also good options to add on the team, as otherwise, Zygarde-C can be severely crippled when switching in if hazards are up.
Thousand Arrows is the main STAB move for this set, as the move can hit every relevant Pokemon in the metagame regardless of their typing. Will-O-Wisp acts as a great way to beat out opposing Chanseys that transform into this set, as they generally do not run a Toxic Orb to take advantage of the effects of Poison Heal. It also helps Zygarde-C cripple physical attackers such as Mega Mewtwo X and Yveltal as well. Sacred Fire can accomplish the same goal most of the time as well and can also hit Steel-types that are not hit super effectively from Ground-type attacks such as Ferrothorn and Kartana. Knock Off can also be used to cripple opposing Eviolite Chansey and Toxic Orb Giratina on the switch in. It also can provide great utility for your team, getting rid of items such as Safety Googles, type plates, and Choice items. King's Shield is a great option to check certain priority users such as Mega Rayquaza and Regigigas by lowering their Attack stat, often forcing them to switch out. It also allows Zygarde-C to gain passive recovery from Poison Heal without fearing to be hit by any attacking moves for one turn. Taunt is a great move to cripple defensive Pokemon that can potentially wall Zygarde-C such as Unaware Mega Audino, Fur Coat Giratina, and Unaware Tapu Fini from recovering or using moves such as Haze that could potentially stop Zygarde-C from sweeping. Dragon Hammer is another option that grants Zygarde-C another STAB move that allows it to deal more damage against other Dragon-types such as Zygarde-C and Giratina, although Poison Heal Zygarde-C is already pressed for moveslots, so it's usually not worth running. Shift Gear is the main setup move on this set, as it allows Zygarde-C to become more of an offensive sweeper.
Poison Heal allows Zygarde-C to recover 12% of its HP each turn while also being immune to other crippling status affects such as burns, which complements physical setup boosting sets immensely. A Toxic Orb is equipped to ensure that Zygarde-C is inflicted with the poisoned status to utilize Poison Heal. EVs are maxed out in every stat besides Special Attack with an Adamant nature to ensure Zygarde-C hits as hard as possible when attacking.
Be careful when swtitching in on certain Core Enforcer users such as Dialga and Giratina, as not only does the move deal super effective damage against Zygarde-C, but it can also nullify the effects from Poison Heal, meaning that Zygarde-C would take poison damage instead of receiving healing. Once the Toxic Orb is activated, Zygarde-C can become a great sponge to annoying attacks such as Knock Off and status moves in general. Try not to set up on certain Unaware walls such as Yveltal, Mega Audino, and Zygarde-C, as these walls can threaten to steal the boosts from Zygarde-C through Spectral Thief and pass them to another physical sweeper on the opposing team. Assault Vest users such as Mega Gyarados and Dialga often carry Spectral Thief as well in combination with powerful attacks that could damage Zygarde-C. Scouting coverage options on offensive Pokemon such as Ice Beam Mega Mewtwo Y and Ice Hammer Primal Groudon is vital when using Zygarde-C, since it holds such a great defensive presence on teambuilding and is often prepared for due to this. Zygarde-C should only try setting up against opposing passive Pokemon that cannot really immobilize it too much such as Aegislash, Giratina, and Solgaleo. If the opposing team pertains an Imposter Chansey, try crippling it first with Will-O-Wisp before setting up, as this allows Zygarde-C to not be threatened by the Chansey even if it starts boosting as well. Try not to be too liberal when using King's Shield against priority users such as Mega Diancie and Kyurem-B, as otherwise, the foe can bait out the use of King's Shield and use another move not affected by it to be able to check Zygarde-C the next turn.
Unaware walls such as Mega Audino, Xerneas, and Yveltal are useful team members, as they can check opposing threats that may have stolen stat boosts from Zygarde-C. They can also check Chansey that have transformed into Zygarde-C if the Zygarde-C on your team does get forced out by it. Pokemon that can check -ate ability users such as Solgaleo, Aegislash, and Soundproof Mega Slowbro can also be useful partners, since they can switch in on powerful -ate attacks that would otherwise dent Zygarde-C. Powerful wallbreakers such as Stakeout Primal Groudon, Steelworker Kartana, Aerilate Mega Rayquaza, and Sheer Force Mega Mewtwo Y are all great partners to break through Unaware walls that would otherwise stop Zygarde-C from sweeping effectively. Bulky Steel-types such as Solgaleo, Registeel, and Magearna can be useful, as they can take on Fairy- and Ice-types that would otherwise threaten Zygarde-C out.
A RegenVest set with Rapid Spin / Core Enforcer / Metal Burst / U-turn is a decent set that allows Zygarde-C to be a specially defensive bulky pivot, but the set gets worn down quite easily by entry hazards such as Spikes and Toxic Spikes, and Zygarde-C cannot really stomach Ice-, Fairy-, and Dragon-type special attacks all too well even with an Assault Vest. A defensive Poison Heal and Magic Bounce set is also quite good, as Zygarde-C gains so much passive recovery from the former and can block status moves with the latter; however, these sets are usually outclassed by better defensive abilities in Unaware and Fur Coat. Stealth Rock is a useful move on all defensive sets, as Zygarde-C gains many chances to set it up thanks to its great bulk. Defensive sets with Darknium Z and Icium Z for Parting Shot and Haze, respectively, can also be used to prevent Zygarde-C from being crippled from Trick users. A Soundproof special sweeping set with Quiver Dance / Thousand Waves / Shore Up / Changling Scales also can work, as it can lure and trap incoming Imposter Chanseys. However, there are several better special sweeping threats that can perform Imposter-proofing shenanigans better such as Mega Gengar, Mega Rayquaza, and Zekrom for this set to actually be that viable. Zygarde-C can honestly run any defensive ability viably due to it possessing possibly the best physical bulk in the entire metagame.