Poison-type Pokémon take double damage from Ground and Psychic-type attacks. However, they only take half damage from Grass, Fighting, Poison, and Bug-type attacks. They take normal damage from all other attack types.
Poison-type moves deal double damage to Grass-type Pokémon. However, they only deal half damage to Poison, Ground, Rock, and Ghost-type Pokémon and don't affect Steel-type Pokémon. They deal normal damage to all other Pokémon types.