Just fyi Poison is the worst offensive typing in the game.
it is only supereffective against:
Non Effective against:
and almost all typing of Poisons is awful:
Grass/Poison- Flying, Ice, Fire, Ground, Psychic
Ghost/Poison- Ghost, Dark, Psychic, Ground
Fighting/Poison- Flying, Ground, Psychic(x4)
the only beneficial Poison combos are:
Resists: Ghost, Grass, Dark
Immune: Psychic, Poison
Neutral: Fighting, Bug, both of which normally kill Dark types.
Poison is an OK type to have as a secondary to block Toxic, but Mono Poison has way too many flaws to be useful outside of NU and the only really threatening Poison types (Tentacruel, Gengar ) are OU.
just food for thought.