Oil snake main design:
Supplementary sketches 1
: Ouroboros transportation, using Sludge Bomb, roasting a Delibird, lurking in waters, some tail-attack (Power Whip?), and sneaking up on a Gastrodon.
Supplementary sketches 2
: Sludge Bombing/Inferno-ing a Celebi, Intimidating a Dugtrio, sleeping (Rest, if as a move), some fanged attack on a Stunfisk, Wild Charge, Coil, and a sequence of igniting its trail of oil with a FWOOSH.
Supplementary art 2.5:
Pixel art version of the first two drawings from sketches #2.
Supplementary sketches 3:
Two-piece set of a coiling oil snake springing up and down for an Earthquake or something, Sludge Wave, Overheat (or Outrage), an affirmation of Dry Skin, preparing a Gunk Shot, Shed Skin as a flavor ability, and a tail-oil-boosted Quick Attack.
Supplementary doodles 4:
Doodles of some of the lesser-lauded concepts that I like--paintseagull's, KoA's, thornchild's, and RotationalBasis's--and the oil snake in more scenarios: some fridge-logic-like thingymabob on how it absorbs Toxic Spikes (looks like it's taking an Ice Shard :/), using Hypnosis on a Politoed (I do keep pokemon to scale, hence it needing to stick the tail in the ground to reach up), and (like Yilx's design) sticking its pump-tail into the ground to use Sludge Wave/Lava Plume/Eruption.