by dashing back and forth, squirtle slingshots around in his shell, with certain timing and doing an upsmash from this turnaround slingshot, you "hydroplane" which is basically snake sliding but with different controls. if you dont charge his neutral b and use it right away, it isnt watergun, but bubble instead. bubble has small range, has multi hits, little to no knockback. but it deals more damage than water gun so yeah,lol. it is also good for a laugh.