* Grass: Grass-type moves deal double damage to Water-type Pokémon.
* Electric: Electric-type moves also deal double damage to Water-type Pokémon.
Here are some common Pokémon with moves that are super effective against Blastoise:
* Grass:
* Bulbasaur: Vine Whip, Razor Leaf
* Oddish: Poison Powder, Razor Leaf
* Bayleef: Razor Leaf, Solar Beam
* Sceptile: Razor Leaf, Leaf Storm
* Grovyle: Razor Leaf, Leaf Storm
* Victreebel: Razor Leaf, Solar Beam
* Roserade: Razor Leaf, Solar Beam
* Electric:
* Pikachu: Thunder Shock, Thunderbolt
* Raichu: Thunderbolt, Thunder
* Magnemite: Thunder Shock, Thunderbolt
* Magneton: Thunder Shock, Thunderbolt
* Electrode: Thunder Shock, Thunderbolt
* Jolteon: Thunder Shock, Thunderbolt
* Manectric: Thunder Shock, Thunderbolt
Note: Blastoise also has a Shell Armor ability, which negates the effect of critical hits. So while these moves will still deal double damage, they're less likely to land a critical hit.