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Megahorn is powerful, fairly accurate, and an excellent STAB or coverage move. Pokemon such as Heracross, Scolipede, and Sawsbuck can use this move to deadly effect, gaining super effective coverage on the myriad Psychic-, Dark-, and Grass-types in OU. Even some resisted targets can be 2HKOed, and Megahorn is a good move for a set backed by Choice Band.
X-Scissor is a weaker, more accurate option.