Qwilfish

Qwilfish, what an odd little pokemon, no evolutions, never really stood out, and looks like it would taste good, who would guess that this odd ball is one of the most threatening rain sweepers in the UU environment, not me. Now Kabutops has better attack, probably better typing, but he doesn't have the ability to absorb toxic spikes, or this much speed, or even the ability to ruin any poke with a simple BOOM. Now I'm not really going to tell you that Qwilfish is better than any other rain dance abuser, but you should definitely not underestimate this beast or else you'll become balloon food.

TerrorFish
Ability: Swift Swim
Item: Life Orb
Adamant/Jolly Nature
252 atk 252 spd 4 hp
-Swords Dance
-Explosion
-Poison Jab
-Waterfall
Now there may not be many options on this set, but it works, and it works well. With Qwilfish's decent speed, even without rain dance he can attempt to sweep, and with rain dance it can mess stuff up. Swords Dance puts your okay attack into a nice 500-600 zone depending on your nature, and with rain dance up it's speed is around 500 too. Now with great attack and speed, if you have anything that can wall this bring it out, but then you loose a poke, cause this bad boys going out with a bang. Swords Dance is obvious, as it really turns you into a sweeper. Explosion is for a last minute bang, or just to get rid or something, which is what gives this balloon an advantage over Kabutops. Waterfall is very hard to deal with rain up, and will usually be your main attack. Poison Jab is for bulky waters, grasses, and other odd walls that try to stop your sweep. Life Orb can be replaced with leftovers, but on this set, Quilfish is only going to come out once (usually) and will probably kill itself with explosion before you get to switch it out. Adamant makes you very scarey, but without rain dance up your max speed is 269, which can be easily revenge killed, but jolly makes your attack stat look a little weak, so either way it's your call.

Qwilead
Ability: Swift Swim/Poison Point
Item: Focus Sash
Adamant/Jolly Nature
252 atk 252 spd 4 hp
-Waterfall
-Toxic Spikes/Spikes
-Explosion/Destiny Bond
-Counter/Aqua Jet/Rain Dance/Poison Jab
Qwilfish may surprise you with an amazing sweep, but how about a nice lead to a game. With decent attack and speed, you can set up some hazards, maybe get in attack, and then make the other lead pay with their own life. This will get you support, and will atleast take out one poke guarenteed. Waterfall is very strong and has a lot of power even with your okay attack, plus STAB. Now here's another debate between Kabutops and Quilfish, you can either use stealth rocks with Kabutops or set up layers of spikes with Qwilfish. Toxic spikes are preferred cause even one layer does damage, where as 1 layer of spikes doesn't really do much, and you usually won't be able to set up 2-3 layers of spikes. Explosion is usually preferred over destiny bond, as it doesn't rely on your opponent as much, but destiny bond works great if your faster. The last move is either attack, or more support with rain Dance. Now if you want this to be a rain dance lead, go ahead, but you might have to do some tweaking on my set, because I think that Qwilfish has more to offer than just a rain dance lead. Counter can get you a good focus sash KO, but it will leave you vulnerable for revenge killing, but if your faster you could OHKO with counter than explode on another poke. Aqua Jet has priority, and STAB and makes you a good anti-lead paired up with support and explosion, however this is very poor coverage, which is where Poison Jab can be used as it has STAB, and it's pretty powerful, and has a chance to poison. The nature again comes down to power or speed. The ability is tricky, if you do decide on rain dance, use swift swim, but if you don't use rain dance poison point might atleast get something poisoned before you go down. The item choice is obvious because your always going to either explode or support with spikes, so focus sash is a no brainer.

BulkyBalloon
Ability: Poison Point
Item: Leftovers
Impish Nature
252 hp 104 sp def 152 def
-Spikes/Toxic Spikes
-Pain Split
-Poison Jab/Waterfall
-Explosion/Counter
Now, this set is no bulky beast of nature, but it does have it's uses. You should usually get atleast 2 sets of spikes set up, and will probably explode killing one of heir guys off. It does have some advantages over Clyoster, and other bulkier pokes, for instance it absorbs toxic ans=d toxic spikes, which helps your team against status, and with explosion or counter, you can actually take a pokemon out with it. Spikes is usually preferred because you will be living longer, which will create more chances to set up, but toxic spikes is still nice to have. Pain split is obvious, and is your only recovery move, and you might get lucky if Chansey comes in =p. Posion Jab has STAB, and hurts usual water and grass switch ins, but if a steel comes in your screwed, so Waterfall is an option too. Explosion is a nice ending move, when you know you can't live any longer, but counter can do the same thing, and your so bulky you can live, and strike back double the damage, which could get you a KO, and allow you to stay alive. Leftovers is obvious, as it heals you some, the EV's give you some decent bulk, and the nature gives you good defense, without hurting your sp def either. Poison Point is usually better, as swift swim is wasted, as you have no speed ev's invested.

He's not the best UU has to offer, but he's not the worst, and deserves some thought of whether he earns a spot on your rain dance/stall/offensive team. Qwilfish definitely needs support to help what it can do. Rain Support is a must for the first set, qwilfish loves a strong grass partner that can hurt other grasses and waters for him. Most importantly for all sets, is that he needs a strong sweeper to clean up what he's blown up on, so that if they live, they will now be dog food for your next sweeper. Usually waters and grasses do nice for countering, grasses be warned, Poison Jab is a KO. Waters are the perfect counter as most set will either try to hurt it with Poison moves, or just waste Qwilfish and just blow up on you. Oddly enough Qwilfish is an excellent counter to Qwilfish, as it is non effective by both types, and the only way past it is with exploding.