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Deals damage. Its Base Power can be anywhere between 1 and 120, depending on the current HP of the target. The formula to determine the Base Power is as follows:
Base Power = 120 * (target's current HP / target's maximum HP), rounded half down, but not less than 1.
The signature move of Regigigas. As the sole user, since Smeargle won't be using this at all, it needs to get rid of the Slow Start effects first to use it at full power. This, however, is a problem with Regigigas and not the move, though the move has plenty of problems of its own. As a move with variable damage, for it to be competitively viable, the maximum power the move can achieve will need to be almost always present, and unfortunately, the move is simply too unreliable to merit any use whatsoever. A Pokemon at 50% health will only be taking a 60 Base Power attack, and thus any reasonably bulky Pokemon will survive easily, where a Return or Frustration attack would have done far more damage.
Return has a higher Base Power and perfect accuracy, making it a much more reliable option.
Double-Edge is a much more powerful alternative; however, it inflicts recoil damage upon the user.
Wring Out is a special equivalent.