While Quagsire is yet another example of a bulky Water-type, it does have a few advantages that put it above the rest. Most notably, its typing grants it only one weakness, Grass-type attacks, and its ability Unaware ignores the opponents' stat boosts; this allows Quagsire to take on physical setup sweepers easily, and simplifies prediction massively, as Quagsire does not have to wearily play around these foes. Quagsire is further aided in this role by its access to Recover. That being said, its defensive prowess is somewhat diminished by its low Special Defense and the fact that its only weakness is a 4x weakness, making its typing a double-edged sword in that respect. Its typing also doesn't give it a large amount of resistances either, meaning that powerful physical attacks will still hurt it. Quagsire also has mediocre offensive stats as well as pathetic Speed, and faces great competition with Clefable, another Unaware user which has an extraordinary movepool and the advantage of being able to take on special attackers better. However, it still holds the advantage of being able to beat the common Bisharp and Mega Charizard X, two Pokemon that Clefable can't hope to beat, giving Quagsire a recognizable niche on stall in the metagame.
name: Physically Defensive
move 1: Scald
move 2: Earthquake
move 3: Recover
move 4: Toxic
evs: 252 HP / 252 Def / 4 SpD
Quagsire's standard set aims to take advantage of it's physical walling capabilities. Scald is an excellent move, and Quagsire has no trouble using it to burn the physical attackers it walls, severely crippling them. Earthquake functions as a STAB move to dent Pokemon such as Mega Charizard X, Tentacruel, and Heatran. Recover is mandatory to heal off the damage from the opponents it walls; without it, Quagsire would not be able to effectively take foes on. Finally, Toxic is a great move to cripple walls and other defensive Pokemon such as Hippowdon, Clefable, and Trevenant. Encore can be used to lock an opponent into a move, giving a teammate a free setup opportunity, such as against a Gyarados's Substitute, a Latias's Defog, or a Garchomp's Earthquake. Ice Beam is Quagsire's hardest hitting option against Pokemon that are 4x weak to Ice-type attacks, such as Salamence, Noivern, and Landorus-T, while Stockpile is a viable option to boost Quagsire's defenses even further, aiding it even more in its walling capabilities.
Because Quagsire's primary role is checking physical attackers, an EV spread of 252 HP / 252 Def is needed to do the most with its otherwise mediocre bulk. A Relaxed nature enhances Quagsire's physical bulk even more, while also not lowering either of Quagsire's offenses. Leftovers is a mandatory item, as it gives Quagsire additional, consistent recovery, which benefits it immensely over time.
Quagsire's main objective is to keep your team safe from physical setup sweepers. Quagsire's Unaware allows the user to not worry as much about setup sweepers, so don't worry if one starts setting up on a teammate, as Quagsire can act as a fail safe. Scald is the move that should be used the most often, unless the opponent has a way of dealing with it, such as Water Absorb or Storm Drain, in which case Toxic is the most optimal choice. Against a Natural Cure user, your best bet is to switch into something which can deal with it. Remember, Quagsire absolutely hates status, so if you predict that the opponent will use a status move such as Will-O-Wisp or Toxic, don't hesitate to switch out. Quagsire needs to be at full health to switch in on physical attackers without the risk of being 2HKOed, so if possible, try to Recover before you switch out. Don't keep trying for a burn with Scald if you need to restore your health with Recover.
Mega Venusaur is a good teammate as it doubly resists the Grass-type attacks that trouble Quagsire, it is able to cripple threats to Quagsire with Sleep Powder, and it can also wall the special attackers that Quagsire has trouble with. Heatran synergizes well into a Fire / Water / Grass stall core with Quagsire and Mega Venusaur, and is adept at walling special attackers. Other Pokemon that can help deal with Quagsire's 4x weakness are recommended, such as Goodra, Scizor, and Ferrothorn. Blissey, Chansey, and Sylveon are also great teammates, as they can remove the status that Quagsire hates with either Aromatherapy or Heal Bell, and they too can deal with the special attackers which beat Quagsire.
A combination of Infestation and Yawn can work to some extent to immobilize foes, creating setup opportunities, but Encore works just as well without taking up two moveslots. Haze is an interesting choice, as it allows Quagsire to check full Baton Pass teams by resetting their stat boosts, but it has little utility outside of that as Unaware prevents the opponents stat boosts from mattering when the Pokemon is targeting Quagsire, so it is therefore quite a niche option. A Curse set with a specially defensive spread can work to boost Quagsire's Defense while also powering up its physical moves, but Quagsire still lacks power even when boosted; if using Curse, Quagsire also lacks coverage. Iron Tail can be used as a coverage option to beat Calm Mind Clefable, but doesn't have much utility outside of this.
Checks & Counters
**Grass-Types**: Quagsire's main counters are Grass-types, as they can hit it for massive damage with their STAB. Good examples in the metagame include Roserade, Breloom, Mega Venusaur, Ferrothorn, Celebi, Amoonguss, Trevenant, and Gourgeist.
**Powerful Special Attackers**: Powerful special attackers can prey on Quagsire's weaker defensive stat and damage it severely. Hydreigon, Choice Specs Noivern, Gengar, and Keldeo are all good examples of Pokemon that can wear it down with their STAB moves.
**Mold Breaker Setup Pokemon**: Excadrill, Haxorus, and Mega Gyarados all have the ability Mold Breaker, which allows them to bypass Quagsire's Unaware ability with offensive boosts they have already gained, meaning that Quagsire cannot wall them.
**Toxic**: Toxic wears Quagsire down quickly and thus prevents it from being able to wall opponents effectively. Blissey, Chansey, and Gliscor are examples of Pokemon that can Toxic Quagsire.
**Taunt**: Taunt is quite bothersome for Quagsire, as the move prevents it from using Recover or any of its other status moves, and users of Taunt such as Gliscor and Sableye can easily take advantage of that.