I have three movesets, all with a variation from the standard Blastoise. These work great because you don't have Earthquake and Dig isn't very good. It is order of what I think is best to worst:
- Offensive and Defensive: Leftovers
Surf: STAB, good power, high accuracy, double damage against diving foes.
Ice Beam: Good power, high accuracy, chance to freeze, used to deal with Grass types.
Mirror Coat: An effective counter to Sp. Attacks, which Blastoise can survive.
Iron Defense: To make sure Blastoise isn't beaten by Physical moves.
- Defensive Behemoth: Leftovers
Toxic: Can't have a defensive set without this can we?
Iron Defense: Makes Blastoise into even more of a defensive behemoth.
Aqua Ring: Heals Blastoise.
Water Spout: So we aren't crippled by Taunt. High power with high HP (which is great with Aqua Ring), STAB, high accuracy, deals with Poison and Steel types who won't be harmed by Toxic.
- Ultimate Offense: Lum Berry
Skull Bash: Increases defense on turn one, then unleashes a high damaging, high accuracy attack onturn two.
Rain Dance: Increases the power of Surf.
Ice Beam: Good power, high accuracy, STAB, chance to freeze, used to deal with Grass types.
Surf: Good power, high accuracy, double damage against diving Pokemon , STAB, powered up by Rain Dance.