Lefties vs Black Sludge: Lefties if you don't want someone else on your team to get black sludge.
Also if Swalot lacks Sticky Hold, which it really has no business doing. Nobody's going to try a draining move on Swalot, Liquid Ooze or no Liquid Ooze. They're Grass moves, and Swalot is a Poison-type.
Now then!
Swalot, an oft-overlooked Poison-type. Not deserving of the lack of attention it's forced to endure, I think. First off, 100/83/83 defenses are nothing to sneeze at. This thing was clearly meant to take hits.
Swalot@Black Sludge
Sticky Hold
Careful nature
252 HP/252 Sp.Def/4 Def
~Curse
~Gunk Shot/Fire Punch/ThunderPunch
~Earthquake
~Rest/Pain Split
The EVs and nature are intended to max out Swalot's special bulk, allowing Curse to do what it does, and beef up Swalot physically. After a Curse or two, Swalot can take physical hits more effectively, and with the upped Attack, can even attempt to sweep. Earthquake has power and coverage, so that's obvious. Gunk Shot gets STAB, and is arguably the most powerful move a Swalot can boast. That said, you run Gunk Shot+Earthquake, Skarmory walls you to hell and back. Of course, since Skarmory is a physical wall, it would do that anyway. Still, Fire Punch and ThunderPunch are decent options if you feel they'll help out against aforementioned steel bird. Now, slight Black Sludge recovery won't sustain Swalot forever- it needs a more reliable form of recovery. What it gets, however, is Rest and Pain Split. Bleh. This one's up to you. Shaky but immediate recovery versus immediate and full recovery followed by two turns of sleep. Your call.
Black Sludge is a given. It's like Leftovers, but for Poison-types only. Sticky Hold prevents the potential issue of a Trick user taking your Black Sludge, then pawning it off on a non-Poison-type teammate of yours. Granted, most of what I use are Poison-types to begin with, so this wouldn't be much of an issue with me, but then again, I'm not most people. Swalot has no business running Liquid Ooze, as the only draining move that anyone would bother using on it is Leech Seed, and that will not compensate for the possibility of Swalot losing its Black Sludge to Trick users.
Swalot@Black Sludge
Modest nature
Sticky Hold
252 Sp.Atk/252 HP/4 Speed
~Stockpile
~Sludge Wave/Venoshock/Protect
~Ice Beam
~Shadow Ball
Poison-types get a bad rep for having bad coverage offensively. This may be admittedly somewhat true, but by no means does it make Poison a bad type. It can still hold its own defensively. Add to that, some Poison-types can still kick butt using the other types of moves they learn. Here's a decent example right here. Stockpile boosts both defenses simultaneously with each use. Swalot's defenses aren't bad by any means, and this only helps them. Sludge Wave is the Poison equivalent of Thunderbolt, Ice Beam, and Flamethrower. Nice and powerful. Alternatively, if you have Toxic Spikes support up, there's no reason to not go with Venoshock, as it will be more powerful against poisoned foes. If you're one of those people who feel that the sheer power of a STAB Poison move doesn't compensate for the crappy coverage, Protect is always an option, allows you to stall for some Black Sludge recovery. And then, for the actual attacking, there's Ice Beam and Shadow Ball. This one's walled by pretty much every Steel-type your opponent can hope to throw at you, but nothing's perfect.
Again, Black Sludge and Sticky Hold are obvious.
Swalot@Black Sludge
Sticky Hold
Careful nature
252 HP/252 Sp.Def/4 Def
~Curse
~Ice Punch
~Sleep Talk
~Rest
Here's the idea. Curse up. Rest when you need recovery. Then spam Sleep Talk like there's no tomorrow! You'll either get Curse (more bulk and power), Ice Punch (the attack; I chose Ice Punch because nothing is immune to it, unlike Gunk Shot, Earthquake, ThunderPunch, and Fire Punch), or Rest (will fail if you're already asleep). Sleep Talk is the glue that holds this set together. It means that Swalot won't be dead weight while it sleeps off injury. Walled by Steel-types, and Ice-types of all things, but then, after enough Curses, an opponent's resistance to Ice will start to become moot as Swalot's attack reaches (g)astronomical levels, making its Ice Punch the equivalent of getting hit by a frozen truck.
And do I really need to explain, AGAIN, why I suggest Black Sludge and Sticky Hold?
