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Deals damage and has a 50% chance to lower the target's Defense by one stage.
This move is only learned by the Cloyster and Samurott lines. It is a useful option on both Water-types, as it is only slightly weaker than Waterfall and the strongest physical STAB move Cloyster has access to. However, the imperfect accuracy makes Waterfall more desirable on Samurott, and Hydro Pump is usually chosen over Razor Shell on Cloyster for its ability to break through physical walls.
Waterfall is a stronger alternative with 80 Base Power.