Generation Iii
Serene Grace
Promotes added effects.
Detailed Effect
This Pokémon's moves have twice their usual effect chance. An effect chance is a move's chance to inflict a status ailment, cause a stat change, or make the target flinch in addition to the move's main effect. For example, Flamethrower's chance of burning the target is doubled, but Protect's chance of success and Air Cutter's increased critical hit rate are unaffected. Secret Power is unaffected.
Pokémon With Serene Grace
15 canonical Pokémon forms can have this Ability.

Chansey
Togepi
Togetic
Dunsparce
Blissey
Jirachi
Happiny
Togekiss
Meloetta Aria
Dudunsparce Two Segment
Shaymin Sky
Meloetta Pirouette 
Dudunsparce Three Segment
Deerling
Sawsbuck