Sir Tankalot
Item: Black Sludge
Ability: Liquid Ooze
Moves:
-Amnesia [Level up]
-Acid Armor [Egg Move- is also an egg move in gen iV]
-Giga Drain [Gen IV TM]
-Toxic [Level up]

Well, basically a tank. Amnesia and Acid Armor raises its defences to really high levels, which, combined with its high HP, will allow it to hang around for a while.
Toxic is to deal damage, which, when combined with Black Sludge and the high defences and HP, will mean he can hang around for a while. Combine that with Giga Drain, which can also deal with ground types which are horrible for this guy to face, and you have a real tank.

Mr. Messy
Item: Focus Sash
Ability: Liquid Ooze
Moves:
-Gastro Acid [Level up]
-Destiny Bond [Egg Move- Koffing/Wheezing]
-Pain Split [Egg moves- Koffing/Wheezing
-Sludge Bomb/Gunk Shot [Level up]

This Swalot is one that is a pain to face. It was Gastro Acid, a potential battle-winning move if used on the right Pokemon. For example, it can allow you to KO a Shedninja with any attack, and more valuable, stop Blaziken and Ninjask from being able to set up a sweeper.
Then you have Destiny Bond. This move guarantees that whatever knocks out Swalot, who has a Focus Sash so he doesn't die before using the move. This can ruin an opponent's strategy, especially if its a boosted sweeper such as Garchomp.
Next, Pain Split. Swalot is low on HP, and you opponent sends out a new Pokemon. This will restore Swalot's HP and make the opponent weaker straight away.
Finally, one of two STAB attacking moves, both of which can inflict poison at a 30% chance. It juts depends on whether you prefer more power or more accuracy.

Thanks for reading.