Sweet Veil prevents the Pokémon with this Ability and its allies (including non-adjacent allies) from falling asleep. Rest will fail when used by the Pokémon with this Ability or an ally, unless it has Mold Breaker, Turboblaze, or Teravolt.
Sweet Veil causes Yawn to fail if used on the Pokémon or its allies (including non-adjacent allies), and prevents the Pokémon and its allies already drowsy due to Yawn from falling asleep.
When a Pokémon with Mold Breaker, Turboblaze, or Teravolt uses a move, the effects of Sweet Veil (including allies') are ignored for the duration of that move. As such, if the move of a Pokémon with one of these Abilities triggers Effect Spore, it will not be protected by Sweet Veil.