Curse + RestTalk (Grimer) @ Leftovers  
Ability: Sticky Hold  
EVs: 252 HP / 4 Def / 252 SpD  
Careful Nature  
- Rest  
- Curse  
- Sludge Bomb  
- Sleep Talk
Optional Move(s): 
- Flamethrower
- Fire Blast
- Thunderbolt
- Ice Punch
- Giga Drain
- Hidden Power [Grass]
- Haze
- Taunt
- Memento
Optional Item(s): 
- N/A
Optional Ability: 
- N/A
Optional EV/IV(s): 
- N/A
Overview: Grimer is a staple on rain teams, thanks in part to its ability to take on Sunflora, which can otherwise be an issue. Its Poison-typing also means that it is Toxic immune, giving it many opportunities to switch in to try to set up and sweep, especially versus common defensive Pokémon like Bayleef and the rising Lileep. 
Curse + RestTalk: This set is best used once all of its answers are taken out, giving the user the best chance to sweep. Curse lets Grimer set up, boosting its great base 80 Attack and HP and fortifying its low Defense. Despite having an equally low Special Defense, investing fully with a Careful nature allows Grimer to take on many of the Grass-types like Lileep, Bayleef, and Sunflora or weaker special attackers like Seaking, Chinchou, Staryu, and Growlithe in the tier. These Pokémon also have low base Defense (bar Bayleef), which means that Grimer can threaten them all without boosts, or use them as set-up fodder and sweep. 
Other Options: Grimer has a surprisingly wide amount of offensive and support options, including Flamethrower and Fire Blast, Thunderbolt, Ice Punch, Giga Drain, Explosion, Haze, Taunt, and Memento. However, its low speed tier, low Special Attack stat, and bulk when uninvested holds it back from effectively using these moves. 
Checks and Counters: This mono-attacking set cannot touch a number of Pokémon in the tier, including Rhyhorn, Dustox, opposing Grimer, Koffing, and Magnemite. Additionally, it is very slow, and without any boosts to its Defense with Curse, very frail on the physical side. This means that faster Pokémon, and many of the physical wallbreakers can threaten to ohko or revenge kill Grimer, namely Aipom, Castform, Rhyhorn, Delibird, Pidgeotto, Taillow, Natu, and Spoink.