Target sleeps at the end of the next turn.

Yawn makes the target Pokémon drowsy. The target will fall asleep at the end of the next turn.
Yawn bypasses accuracy and evasion checks to always hit except when the target is in the semi-invulnerable turn of moves such as Dig or Fly.
Pokémon with the ability Insomnia, Vital Spirit, Shields Down (with the shield active), or Comatose are immune to sleep.
Yawn fails against targets without Soundproof during the effects of Uproar.
If used after the uproar has already started, the target can still become drowsy.