Strong ground and psychic Pokemon such as Claydol, Metagross, and Tyranitar.
Both ground and psychic moves are super-effective against poison. They are both multiplied by 2. A good ground type move is earthquake, but since many poison Pokemon have levitate or are flying, they can avoid this.
It depends on dual types, abilities, available moves, etc., of both Pokemon, but the strongest Pokemon against poison Pokemon generally would be the strongest psychic and ground Pokemon. Some excellent psychic and ground Pokemon (strongest is quite subjective, so there's no definite answer) are Metagross and Tyranitar, respectively. Claydol is a strong Psychic and Ground dual-type Pokemon.
There are many Water Type Pokemon in Pokemon Platinum, however, there is only one strongest one. That Pokemon is Palkia. Palkia is one of the Main Storyline Legendaries in Pokemon Pearl, it is a Water/Dragon Type. If you are looking for the strongest Non-Legendary, your best bet is Gyarados. Any exceptions?
Skorupi is a Poison/Bug-type Pokemon.
Toxicroak is a Poison and Fighting type pokemon.
Dimethylmercury?
I think fire and flying are good against nature type pokemon!!
Roselia is a Grass and Poison type pokemon.
Crobat is a Poison and Flying type pokemon.
Poison type Pokemon are weak to psychic and ground type moves.
ground and physic Pokemon are super effective against poison Pokemon
Drapion is a poison type Pokemon
Swalot is a Poison type pokemon.
Gulpin is a Poison type pokemon.
Trubbish is a Poison type pokemon.
Garbador is a Poison type pokemon.
Seviper is a Poison type pokemon.
poison-bug. weaknesses are fire rock psychic flying.
Electric