Quagsire has a great defensive typing and an excellent support movepool, but what really sets Quagsire apart from the other standard UU bulky Water-types, such as Milotic and Slowbro, is its ability, Water Absorb. Having Water Absorb allows Quagsire to take on threats like Choice Band Azumarill and Swords Dance Feraligatr without the fear of eating boosted Water-type moves. Another advantage Quagsire boasts over its fellow Water-types is an immunity to Electric-type moves, making it a good counter to Choiced Magneton and Rotom locked into Thunderbolt. Quagsire also has access to Encore, giving it the advantage of being able to ruin any Pokemon that attempts to set up or use supporting moves; this makes up for Quagsire's lack of offensive power, and prevents it from becoming complete set up bait.
Quagsire makes an excellent defensive Pokemon due to its great typing and ability. Thanks to its Water / Ground typing, Quagsire has resistances to Fire-, Poison-, Rock-, and Steel-type moves, immunities to Electric- and Water-type moves (due to Water Absorb), and a lone 4x weakness to Grass-type moves. With Recover and its high HP and Defense stats, Quagsire is able to stall out opponents and take repeated hits without trouble. During this time, Quagsire can support its teammates and cripple opposing Pokemon with its great support options. Earthquake and Waterfall provide reliable STAB attacks and have good type coverage together, netting solid damage on most of the UU tier. Alternatively, Stone Edge may be used to hit Flying-types harder, though the only notable ones that Waterfall does not already hit for at least neutral damage are Mantine and Altaria.Team Options & Additional Comments >>>
Quagsire has access to an overlooked stat-boosting move, Curse, which allows it to boost its average Attack and Defense stats. A base 65 Special Defense stat doesn't look too impressive at first glance, but with immunities to the commonly used Electric- and Water-type moves and only one weakness in Grass-type attacks, Quagsire can be tough to take down after a few boosts from Curse. After a couple of Curses, Quagsire becomes a fearsome tank, capable of tearing holes in any Pokemon that don't resist or aren't immune to its STAB Earthquake. Curse is a given on this set to boost Quagsire's Attack and Defense, Recover allows Quagsire to restore half of its HP in a single turn, and Earthquake and Waterfall provide Quagsire with powerful STAB moves that hit most threats in UU for at least neutral damage. Stone Edge can be used over Waterfall to hit Flying-types for super effective damage, but Waterfall provides better overall type coverage.Team Options & Additional Comments >>>
Quagsire has a variety of alternative options available. Counter is an option to surprise powerful physical attackers that often fail to KO Quagsire in one shot. Body Slam is available if you wish to abuse its 30% paralysis rate, which could be helpful for crippling faster opponents. Finally, Quagsire is one of the few Pokemon with the move Haze; however, while it may be helpful for removing stat boosts, Quagsire is outclassed by Pokemon such as Weezing and Milotic in this respect. You may choose to use Surf on the Bulky Water set, as it hits Rhyperior and Donphan harder than Waterfall, although Quagsire would then need to use a Relaxed nature, allowing Slowbro to almost always outpace it.
If status moves are a major problem for your team, Quagsire may run a set of Curse, Waterfall, Rest, and Sleep Talk. This allows Quagsire to set up on and remain healthy against opponents that rely on status-inducing moves to wear down Quagsire, such as Weezing. Waterfall is the attacking move of choice, as it gives Quagsire a great STAB attack that nothing is immune to (outside of Pokemon with Water Absorb or Dry Skin and Shedinja).
Checks and Counters
Grass-type Pokemon are great counters for Quagsire, as they are able to hit it for 4x super effective damage while also resisting Quagsire's STAB moves. Venusaur is the best counter to any Quagsire set; Sleep Powder and Power Whip both cripple Quagsire beyond repair. Tangrowth makes another great counter to all sets, as it takes little damage from Ice Punch while being able to KO Quagsire with Power Whip. Outside of Grass-types, bulky Water-types cause problems for Quagsire since it is unable to deal great amounts of damage to such foes with any of its moves. Blastoise and Milotic are great options, as they are able to switch in on any of Quagsire's moves and proceed to poison it with Toxic or hit it with Hidden Power Grass, with Milotic being the better of the two as it can Recover until Quagsire is unable to survive the damage from poison. All bulky Water-types that lack Rest need to watch out for Quagsire's own Toxic, however, as it could potentially cripple them for the remainder of the battle.
Weezing and Mismagius make great counters to Quagsire, as they can both switch into Earthquake without worry thanks to Levitate and proceed to burn it with Will-O-Wisp. When Quagsire's Attack stat is reduced from burn status, frail sweepers such as Alakazam and Absol can switch in and set up. Quagsire can be beaten by most Encore users; Jumpluff and Clefable are the most reliable in this regard. They can switch in and use Encore as Quagsire uses Curse or Recover, forcing Quagsire to switch out. This also gives a free turn for Jumpluff to set up Leech Seed or Clefable to set up Stealth Rock. Clefable also has the advantage of being able to switch in on Toxic, as its Magic Guard ability prevents damage from harmful status effects.
Pokemon with Trick can spell doom for Quagsire. Rotom is a great choice, sporting an immunity to Earthquake. This allows Rotom to switch to a Pokemon that doesn't mind the move Quagsire is using, then set up for free as Quagsire switches out. Clefable is another excellent option, as it is able to switch its Toxic or Flame Orb with Quagsire’s Leftovers and cripple Quagsire for the remainder of the match.