Poison

Poison moves are ×2 against Grass and Fairy; Poison Pokémon resist Bug, Fairy, Fighting, Grass and Poison, and are weak to Ground and Psychic.

Look up the type matchup matrix View defense in the matrix

Two-way summary

When attacking

×2 Deals more damage: Grass
Fairy
×½ Deals less damage: Poison
Ground
Rock
Ghost
×0 Deals no damage: Steel
×1 Deals normal damage: 11 types take normal damage — see the full table below

When defending

×2 Takes more damage: Ground
Psychic
×½ Takes less damage: Grass
Fighting
Poison
Bug
Fairy
×1 Takes normal damage: 11 types deal normal damage — see the full table below

These multipliers describe how a move interacts with the defending type in the current reference chart; they are not final damage and have not been verified for Pokémon Champions.

×2 Super effective
×1 Normal damage
×½ Not very effective
×0 Immune

How does adding Poison change things?

moves

Mega Blastoise

Mega Blastoise

Water

Multiplier on Water: ×1
Result: ×1

Toxapex

Toxapex

Multiplier on Poison: ×½
Multiplier on Water: ×1
Result: ×½