Swampert(water) for A rank.
Swampert @ Leftovers
Ability: Torrent
EVs: 252 HP 252 DEF 4 ATK/4SPATK
Impish/Bold nature
-Stealth Rock
-Earthquake/Earth Power/Protect
-Waterfall/Scald/Protect/Roar
-Roar/Toxic/Yawn
Swampert is a great pokemon with great stats and great utility movepool, although it doesnt have any reliable recovery. This set rolls around stealth rock with 3 filler moves tbh. If you decide to go special use 4 SPATK EVs and Bold nature, scald + stealth rock + toxic + filler is my personal preference for moves,but you can vary different sets between the moves in the set.If you decide to use physical, run 4 ATK EVs and impish nature, stealth rock + earthquake + waterfall/Protect + Roar/Toxic/Yawn is the way to go. Yawn is a really useful move because it can force the switch and allow you to setup stealth rock while the opponent wastes a turn switching, after that, you can yawn spam, forcing lots of switches and causing damage with stealth rock, or putting something to sleep. While the opponent is asleep you can also roar predicting a switch and getting even more residual damage. If you dont run any of the 2 moves above, protect + toxic can be used to toxic stall or waterfall + toxic to dual residual damage and hit flying types such as gliscor or aerodactyl.
Swampert @ Choice Band
Ability: Torrent
EVs: 252 HP 252 ATK 4 SPDEF
Adamant nature
-Waterfall
-Earthquake
-Ice Punch
-Stone Edge/Superpower
Utilising its great attack stat, Choice Band can work very efficiently with swampert, as it contains a good offensive movepool to cover alot of types such as flying,dragon,steel,dark,bug,etc.
Swampert @ Leftovers/Damp Rock
Ability: Hydration
EVs: 252 HP 252 SPDEF 4 ATK
Impish nature
-Rest
-Waterfall
-Curse
-Earthquake/Rain Dance
This is Swamperts most gimmick set, but if you have the right support it works efficiently and can late-game sweep after your opponents special attacker with a grass move is gone. Politoed really aids this set but it doesnt entirely depend on it, as running rain dance is a viable option and with swamperts bulk, its guaranteed that it will take any hit that isnt supereffective. I would go as far as saying that this is a physical crocune set, but for swampert, and not having to rely on sleep talk.
Why should it be A rank? As i said before, it has great stats overall,not bad versatility,great movepool, and marvelous typing, having that handy electric immunity.Alot of people say swampert is outclassed by quagsire, but it functions diferently and has better stats. While quagsire has recover,stockpile and unaware working as a staller, swampert has stealth rock,better bulk,better attak stat and a better offensive movepool. Swampert can be predictable, and thats what makes the last 2 sets shine. People usually expect a stealth rock set, but if you bring swampert in on the right mon with the hydration or the band set, it can work wonders, and if you get a curse up, it might start a sweep. What holds back swampert, is the fact that its slow and has a dreadful 4x grass weakness, being easily revenge killed by any pokemon carrying a grass type move. However, if you have the choice band set, and if you predict correctly,nothing can come in safely, and thats why i think it deserves A rank on mono water.