I'm not sure if anyone really knows this Quagsire set, but it stops boosting sweepers in their tracks and in turn sets up on them.
Quagsire @ Leftovers
Trait: Unaware
EVs: 252 HP / 4 Def / 252 SDef
Careful Nature
- Waterfall
- Earthquake
- Recover
- Curse
With the Unaware ability, Quagsire can stop Pokemon that has set up a few boosts from sweeping your team. Maybe a +6 Attack Terrakion is sweeping your team, or a +6 SpA Latias? Here are some calcs.
252 Atk Terrakion Close Combat vs. 252 HP / 4 Def Quagsire: 222-262 (56.34 - 66.49%) -- guaranteed 2HKO
4 SpA Latias Dragon Pulse vs. 252 HP / 252+ SpD Quagsire: 100-118 (25.38 - 29.94%) -- possible 4HKO
252+ Atk Conkeldurr Drain Punch vs. 252 HP / 4 Def Quagsire: 162-192 (41.11 - 48.73%) -- guaranteed 3HKO
252 SpA Thundurus-T Focus Blast vs. 252 HP / 252+ SpD Quagsire: 134-158 (34.01 - 40.1%) -- 39.67% chance to 3HKO
4 SpA Jirachi Flash Cannon vs. 252 HP / 252+ SpD Quagsire: 41-48 (10.4 - 12.18%) -- 9HKO at best
These are but a few of the many calcs that relate to Quagsire. As you can see, Quagsire takes these Pokemon's hits like nothing and can just Recover + Curse stall them. In the end, Quagsire can very well end up doing a lot for your team. A CC from Terrakion only 2HKOs. During which, Quagsire can Recover stall and proceed to Waterfall after Terrakion's defence has been reduced greatly. Waterfall and Earthquake are the standard coverage options for Quagsire. Recover gives Quagsire stalling capabilities while Curse allows Quagsire to set up on Pokemon that can't hurt him.
Here is another moveset that I wouldn't really recommend over the Curse set but it works a few times too. This is more of a stalling set.
Quagsire @ Leftovers
Trait: Unaware
EVs: 252 HP / 252 Def / 4 SDef
Relaxed Nature
- Scald
- Recover
- Stockpile
- Earthquake / Toxic
This set aims to stop boosting physical sweepers and in turn set up on them. Stockpile allows you to set up +3 on both the defensive and specially defensive sides. Scald is used to burn physical attackers and maybe get some residual damage off on other pokemon. Recover is to get back your lost HP. On the last slot, it is based on preference. Earthquake gives you better coverage against Pokemon that resist water-type attacks while Toxic allows you to wear down other stall Pokemon or Pokemon that attempt to set up on you. It might not be a very good option though, as you have another status-inducing move by the name of "Scald".