Venusaur @ Venusaurite
Ability: Chlorophyll (Thick Fat)
EVs: something balky
Bold / Calm Nature
- Strange Seed
- Protect
- Sludge Bomb
- Hidden Power Fire
Strange Seed is a pseudo Toxic and Leech Seed all rolled into one with the huge bonus in "toxifying" Steel-types. Leech Seed already couldn't hit Grass-types so there's no loss there, plus Venusaur has Poison STAB to hit any. HP Fire gets a SE hit on things like Ferrothorn that would otherwise hard wall this set. Protect doubles as HP replenishment and "toxic" damage all in one, putting the opponent one turn closer to fainting and buying you a turn to recover health.
The drawback of using Strange Seed is its rate of recovery/HP damage, which needs at least three turns to harm the target as much as Leech Seed, and most targets switch before then. However, it should be used to put a timer on the foe, something normal Leech Seed doesn't do. Losing 12.5% of your HP per turn is annoying, but there are Pokemon that can offset that loss with Leftovers and a good recovery move once in a while. Strange Seed takes that off the table - the opponent will faint eventually, and staying in longer just heals up Venusaur even more. This trait alone makes it a reliable wincon under the right circumstances and your opponent would have to answer this question: Can you beat it 1v1 without a Flying or Psychic attack? If not, they must preserve their Flying and Psychic Pokemon at all costs or fall to the STRANGE SEED.