Qwilfish

Swift Swim
Speed doubles in rain.
Poison Point
Enemies' contact moves have a 30% chance of poisoning them.
Type Tier
Water / Poison UU
Statistics
Min- Min Max Max+
HP
65
- 271 334 -
Atk
95
203 226 289 317
Def
75
167 186 249 273
SpA
55
131 146 209 229
SpD
55
131 146 209 229
Spe
85
185 206 269 295
Name Item Ability Nature

Swords Dancer

Life Orb Swift Swim Adamant / Jolly
Moveset EVs
~ Swords Dance
~ Waterfall
~ Poison Jab
~ Thunder Wave / Explosion / Return
252 Atk / 4 Def / 252 Spe

This plays like a less powerful, but slightly faster version of Kabutops. Waterfall is your main attack here, with Poison Jab to hit Grass-types and other Waters. Thunder Wave is good to throw around early on, to try and cripple a few faster Pokemon who can stand in the way of a sweep. If you're providing Rain Dance support, then Thunder Wave isn't necessary. Explosion takes out anything that doesn't resist it after a Swords Dance. Return helps against other Qwilfish and Toxicroak, but makes this somewhat inferior to Kabutops. Better to stick with Qwilfish's advantages and go with Thunder Wave or Explosion.

Name Item Ability Nature

Rain Dance

Focus Sash / Damp Rock Swift Swim Adamant
Moveset EVs
~ Rain Dance
~ Waterfall
~ Poison Jab / Taunt
~ Explosion
4 HP / 252 Atk / 252 Spe

The idea is to set up Rain Dance and attempt a sweep on your own, or Explode on something and send in your secondary Swift Swimmer unharmed. With Focus Sash, you will always survive a hit and get Rain Dance on the field, although Damp Rock prolongs the weather. Poison Jab is better for sweeping, but Taunt has its uses too. You can prevent opponent setting up a Sub or throwing status around, which can harm a team members chance of sweeping.

Name Item Nature

Spikes Support

Leftovers Adamant
Moveset EVs
~ Spikes
~ Waterfall
~ Poison Jab / Thunder Wave
~ Explosion / Destiny Bond
252 HP / 252 Atk / 6 Spe

The handy thing about Qwilfish is that four of the best spinners in UU have trouble switching into it, allowing Qwilfish to set up quite easily. Claydol, Sandslash, and Torkoal are weak to Waterfall, and are therefore unlikely to switch-in, while Blastoise has trouble doing any real damage and gets worn down by Poison Jab. Poison Jab helps against Grass-types and Water resistant Flying-types, like Mantine and Altaria. Thunder Wave offers status support and helps to get more from the 30% flinch rate of Waterfall. Finally, Qwilfish can simply Explode when it is no longer needed. Destiny Bond is a good alternative, and might cause some switching if you reveal it early. Don't use it with Thunder Wave though, as full paralysis can spoil the surprise.

Name Item Ability Nature

Choice Bander

Choice Band Swift Swim Adamant
Moveset EVs
~ Waterfall / Aqua Tail
~ Poison Jab
~ Return
~ Explosion
6 HP / 252 Atk / 252 Spe

You can afford to use Aqua Tail here, since you're usually trying to hit Pokemon on the switch, meaning that missing will be less of a problem. Just hit what you can and Explode when you're done.

Other Options

Toxic Spikes is an option over Spikes, although in UU there are many Poison-types who can easily absorb them. There's Endure/Sub and Flail, but that is better left to Kabutops. Natural Gift and a Liechi Berry gives you an 80 BP Grass attack to hit Quagsire. Anything else of note requires Qwilfish to take a hit or be slow (Revenge, Payback, Gyro Ball), which is definitely not acceptable.

Opinion

Qwilfish is a neat UU Pokémon that can support a team, take down opponents by sacrificing itself, or even sweep. It doesn't have the power of other Swift Swimmers like Kabutops and Gorebyss, but it has plenty in its movepool to offer. DP hasn't changed it a whole lot, but there's still enough to recommend.

Counters

Quagsire, Gastrodon, and Whiscash are effective general counters. Walrein and Cradily with Earthquake will also be effective. Most healthy Pokémon with decent defenses will be able to take a hit if they're not weak to Water or Poison, at which point most strong moves will deal a large amount of damage. Further, Qwilfish's Speed is noticeably average, so the non-Rain Dance version can be outsped and hit with strong attacks from Choice item users.