My submission for a creative moveset is a Sub Punching MixPert. Firstly his max stats are based on IVs being 31 across the board.
Swampert @ Leftovers
Relaxed
404/256/216/219/293/140
252hp/52s.atk/204s.def
Substitute
Focus Punch
Surf / Hydro Pump
Roar
This is a somewhat unique Swampert set in that he's set up as a Sub-Puncher. With 101 Subs, his Subs live through Seismic Toss and retaliate with a Focus Punch to Blissey's face.
Swampert vs. Blissey, Focus Punch deals avg 78% dmg
Swampert vs. Infernape, Surf deals avg 63% dmg (80%-94% in Torrent)
Swampert vs. Infernape, Hydro Pump deals avg 75.3% dmg (104%-122% in Torrent)
Swampert vs. Gengar, Surf deals avg 33.3% dmg (42%-50% in Torrent)
Swampert vs. Gengar, Hydro Pump deals avg 38.7% dmg (54%-63% in Torrent)
Swampert vs. Skarmory, Hydro Pump deals avg 42% dmg (54%-63% in Torrent)
Gengar vs. Swampert, Energy Ball deals max 91% dmg
Infernape vs. Swampert, Grass Knot deals max 78% dmg
That means that with Stealth Rock dealing 25% damage to Blissey on the switch in, Blissey retaliating with Siesmic Toss, and then getting OHKO'd by the Focus Punch.
Surf is there so that Swampert has the capability of retaliating against the inevitable Infernape Counter. Grass Knot at 180.6lbs has only 80 power vs. Swampert so the typical Infernape set hits Swampert for 78% whereas Gengar's Energy Ball hits 91%
Grass Knot hits Swampert for 315 damage maximum. at 404hp followed by Leftovers recovery (25.25hp) that gives Swampert 114.25hp enough to drop a Substitute. The next move of Infernape will break the Sub and then Swampert's Surf will deal 94% damage with Torrent which combined with Stealth Rock equals a OHKO if Swampert never attacked before.
Energy Ball from Gengar deals 91% damage to Swampert, and after Leftovers recovery it will on avg. leave him with only 62hp roughly. This however should be avoided at all costs. Should Gengar come in on Swampert to fling Energy Balls, you cannot compete with Gengar. Sub will most likely be up, at which point you can Roar and incur Stealth Rock damage. If Sub is not up, know that Swampert can survive only one hit from Gengar and his move must be Roar. Gengar will go first and then get Roared out. Swampert will barely survive and may need a Wish otherwise it is essentialy fainted.
Hydro Pump on avg will deal on avg of 42% dmg or 63% damage in Torrent to a fully Def EVed Skarmory. With Stealth Rock, two Hydro Pumps will 2HKO to the steel bird, it is then possible to defeat Skarmory should you need to do so, keep in mind however, Hydro Pump is innacurate and you must hit twice to be effective.
The Strategy for SubPert is first, know what you are fighting against. Swampert is good at picking off Walls, hiding from those status conditions using Substitute (In this case, Twave Blissey is useless vs. Swampert, and Sub eats a Toxic), and then striking back with Focus Punches behind Bulky Subs.