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Deals damage and has a 10% chance to lower the target's Speed one stage.
BubbleBeam should generally not be used competitively, as its Base Power is much lower than those of Surf and Hydro Pump, and its secondary effect is neither likely to occur nor especially useful when it does.
Surf is a more powerful and reliable alternative with no added effect.
Hydro Pump is a far more powerful alternative with lower accuracy.