In battle
Serene Grace will double the chance of a move having an additional effect. For example, Psychic will have a 20% chance of lowering the target's Special Defense stat instead of its usual 10% chance, and Rock Smash will always lower an opponent's Defense by 1 level, as opposed to having a 50% chance of doing so.
Serene Grace has no effect on status moves.
Generations III and IV
The 10% flinch chance due to King's Rock and Razor Fang is unaffected by Serene Grace.
Generation V onwards
Serene Grace boosts the 10% flinch chance due to King's Rock or Razor Fang to 20%.
Serene Grace is cumulative with the rainbow produced by using Fire Pledge and Water Pledge on the same turn (causing secondary effect probabilities to be multiplied by 4 if both modifiers are present), except that moves with a chance to flinch will only have that chance doubled once.
From Generation V until Pokémon Sword and Shield (except Abilities are unavailable in Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!), if the user has Serene Grace and uses Charge Beam while its side is under the effect of the rainbow from the combination of Fire Pledge and Water Pledge, the additional effect chance for Charge Beam will overflow and become 24%.
Serene Grace does not increase the probabilities for additional effects of G-Max Replenish or G-Max Snooze.
Affected moves
The table below lists the moves affected by Serene Grace, as well as the Pokémon that can have Serene Grace and learn those moves.
Although the following moves are affected by the Ability, they currently cannot be learned by any Pokémon with Serene Grace. They may, however, be called via Metronome, Mirror Move, Copycat, or Mimic, or be used by a Pokémon that gained Serene Grace by Trace or a move such as Skill Swap or Role Play.
Outside of battle
In Pokémon HeartGold and SoulSilver only, if a Pokémon with Serene Grace breaks a rock and finds an item, the game will instead pick the item below it in the game's list, unless it was the 5% item (this effectively means it will never find the most common item).