What is posion good against Pokemon?

There is no Pokémon type called "posion". You might be thinking of Poison.

Poison-type Pokémon are strong against:

* Grass

* Fairy

* Fighting

Poison-type Pokémon are weak against:

* Ground

* Psychic

* Ghost

* Rock

* Bug

Note: Poison-type Pokémon are not very effective against Steel and Poison types.