Butterfree is weak to the following types of moves:

• Rock (4× weakness)
• Fire (2× weakness)
• Electric (2× weakness)
• Ice (2× weakness)
• Flying (2× weakness)

The strongest weakness is rock-type moves, while fire, electric, ice, and flying moves also deal double damage to Butterfree due to its Bug/Flying typing. This information applies to both regular Butterfree and its Gigantamax form in Pokémon games. So, to counter Butterfree effectively, use Pokémon with moves of these types.