The point of this deck is to use Blastoise's Pokemon Power Rain Dance to be able to rapidly attach water energies to your Pokemon.
This becomes especially powerful when combined with Pokemon Center and Energy Flow - since you can pull all your energies from all your Water Pokemon into your hand with Energy Flow, use Pokemon Center to heal everything, then re-attach them all with Rain Dance.
Kingdra's Dragon Tornado is basically 50dmg + a Gust of Wind, so if that gets online it is VERY disruptive and powerful, and the 30dmg Agility is also very strong to help it shrug off damage retaliation.