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The player may record a sound using the microphone, which will play during the attack. Deals damage, and this move has an X% chance to confuse the target, where X is 0 unless the user is a Chatot that hasn't Transformed. If the user is a Chatot, X is 0 or 10 depending on the volume of Chatot's recorded cry, if any; 0 for a low volume or no recording, 10 for a medium to high volume recording. In Smogon's official tiers, the effect chance is always taken to be 10%. Pokemon with the ability Soundproof are immune.
Being truly exclusive to Chatot, a Pokemon with generally poor stats, this move is very rarely seen. Also, the move itself is not particularly powerful, and though its secondary effect is useful, it is hardly game-breaking. Therefore, even if you have an irresistible urge to use Chatot for some reason, it is probably best that you decline to use Chatter, and instead opt for the more powerful Hyper Voice alongside coverage moves such as Heat Wave and Hidden Power.
Air Slash is a stronger alternative with a chance to flinch the opponent.