Quagsire has all it needs to be a threat in the UU metagame; its great defensive typing leaves it weak to only Grass-type moves, and its respectable physical Defense and HP stats allow it to be a good wall. Recover allows Quagsire to effectively stall Pokemon out with Toxic and prevent foes from KOing it easily. Quagsire's ability, Unaware, is amazing; it allows Quagsire to ignore opposing setup sweepers' boosts. One of Quagsire's main selling points, however, is its ability to check Lucario and either cripple it or hit it hard with Earthquake, which not many Pokemon in the tier can do.
Quagsire's flaws, however, are very exploitable. Its abysmal Speed stat makes it very hard to use Recover effectively to PP stall; it also makes it hard for Quagsire to find turns to use Toxic. Quagsire also cannot take many special attacks due to its low Special Defense stat. Like all walls, Quagsire is also very prone to status, such as burns and poison, which are commonly found in the tier, as they wear it down very easily. While Quagsire can be physically bulky with investment, powerful attackers can still power through it, which detracts a bit from using it as a wall. Quagsire also faces competition from Swampert, which has a better offensive presence, access to Stealth Rock, and more bulk, whereas Quagsire only has Unaware and Recover over it.
move 1: Scald
move 2: Earthquake
move 3: Toxic
move 4: Recover
evs: 252 HP / 252 Def / 4 SpD
Scald has a high burn chance, allowing Quagsire to potentially cripple opposing physical sweepers or wear down special attackers. Earthquake is a STAB attack used to wear down the opponent, and it is Quagsire's primary source of damage in general. Toxic is able to cripple Grass-type switch-ins, as well as opposing walls such as Blissey, which either are forced to switch out or have to stay in and take Toxic damage. Recover helps to Toxic stall and is a form of reliable recovery. Although Quagsire is too slow to use it, Encore is an option to cripple opposing leads.
252 HP EVs add to Quagsire's overall bulk, allowing it to sponge hits with more ease. 252 Defense EVs allow Quagsire to sponge physical hits much more easily. A Relaxed nature is used to maximize Quagsire's Defense completely. Leftovers provide passive recovery. Unaware is the best ability for Quagsire, as it stops opposing setup sweepers or defense-boosting Pokemon from making use of their boosts.
Quagsire does a great job just spreading status throughout the match, whether it's a burn from Scald or poison from Toxic. Due to Quagsire's high Defense, it can easily switch into physical attackers such Mega Aerodactyl, force them out, and cripple the switch-in with Toxic. Quagsire should avoid status at all times, as Toxic or burn damage will easily cripple Quagsire. Predict accordingly when using Recover, and do not spam Scald just to fish for a burn if you need to heal up.
Quagsire works best on stall teams that are weak to setup sweepers. Pokemon that can sponge Grass-type attacks, such as Mega Ampharos, defensive Crobat, Rotom-H, and Chesnaught, are all great teammates, as they also have good defensive synergy with Quagsire and are able to give most opposing Grass-types a hard time. Clerics are incredibly important, as any form of status will instantly make it harder for Quagsire to stall with Recover correctly, and Toxic damage will stack up; Florges and Blissey are great partners to remedy this. Special walls such as the aforementioned Florges and Blissey form a good defensive core with Quagsire, as Quagsire takes physical hits and Florges and Blissey can take special hits.
The majority of Quagsire's other options are inferior to the given set or are just uncompetitive. Quagsire can run a Curse set, but it's too slow, not too bulky, still weak after setting up, and outclassed by regular Quagsire. Yawn can force switches or put the opponent to sleep. Ice Punch can hit Flygon, Noivern, and Crobat for good damage. Water Absorb is a barely usable ability, but it can be used to gain an immunity; however, Water Absorb Quagsire is outclassed by Gastrodon. Lastly, Haze can remove stat changes, but it is quite redundant when Unaware is taken into the equation.
Checks & Counters
**Grass-types**: Quagsire has a quadruple weakness to Grass-type attacks, making Grass-types effective checks to Quagsire. Common Grass-types in the tier, such as Roserade, can either set up hazards or just KO Quagsire. Shaymin, in particular, is a good check to Quagsire, as it resists both of Quagsire's STAB moves and has Natural Cure to negate Toxic.
**Status**: Most status ailments can gradually wear down Quagsire and make it very vulnerable. Toxic in particular is a problem, as it stacks up in damage.
**Taunt**: Taunt easily stops Quagsire from using Recover or Toxic, a bunch from Quagsire's utility as a physical wall.
**Special Attackers**: Any strong special attack will easily take a huge chunk out of Quagsire, due to its mediocre Special Defense.
**Strong Physical Attackers**: Despite Quagsire's defensive investment, powerful physical attackers such as Choice Band Mienshao and Choice Band Haxorus can easily plow through Quagsire.