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Deals damage and always hits twice unless the target is KOed by the first hit. Each hit is treated as a separate attack, and thus abilities such as Weak Armor will activate twice, and this move can KO through Focus Sash and Sturdy. If the first hit breaks a Substitute, the attack will continue to damage the target. Each hit has a separate flinch rate if used with King's Rock or Stench, and a separate critical hit chance. If the target holds a Shuca, Jaboca, or Enigma Berry, it will only affect the first hit of this move. However, the items Life Orb and Metronome treat both hits as a single attack, and Color Change will only activate on the second hit of the move.
Bonemerang is a very decent move, though it is almost never seen as only Smeargle and the rare Marowak learn it. Even then, Earthquake is generally preferred as a Ground-type attack due to its superior accuracy, though Bonemerang is certainly useful for breaking through Substitutes, as well as Focus Sash and Sturdy.
Earthquake is a 100 Base Power, 100% accurate alternative with no added effect.
Gear Grind is a less accurate Steel-type equivalent.