Attack & Unite Move Blastoise - velkhana
This build is more focused on damage but is still tanky.
Build Path

Water GunFirst Pick
Damage. Displacement. Slow.

Water Spout
Area damage. Area of Denial. Slow.

Rapid Spin
Damage. Movement Speed up.

Hydro TyphoonUNITE
Area Damage. Shield. Displacement.
Stat Boosts
Shield (Upon Unite)
Sp. Attack (Upon Goal)
Unite Move Damage Increase
Guide
Try and get to level 9 ASAP. Blastoise's Unite move is one of the best in the game and very good for team fights. Also, you do not want to be the classic Wartortle that still hasn't evolved at 3:00 minutes left of the game.
Eject button is the best held item because you can move your Unite and hit more people, which is the ideal situation for Blastoise.
This build is more focused on attack, the other build Hydro Pump and Surf is also good and applies very long stuns.
Other good held items are Slick Spoon and Focus Band. You could double stack with Aeos Cookie. Top lane is typically easier to stack but the bottom lane is still good since there is more experience.
Works Well With

Blastoise needs a lot of experience and supports are great since they typically run Exp. Share. Eldegoss is a good laner and has a good early game to help Blastoise.
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There are indeed many ways to play Blastoise in Pokemon Unite, and you can find more builds here, as well as detailed information about Blastoise's moves and the items you can assign to it.
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