Change your preferences here.
All stat changes applied to the wielder are doubled. Set boosts (such as those received by Baton Pass or copied via Psych Up) are not doubled. Pokemon with Simple are still limited to a maximum of 6 boosts to any given stat.
No Pokemon that are decent in OU these days have Simple, so while it is a fantastic ability, no Pokemon can take advantage of it. Furthermore, it does not double the effects of existing stat boosts, so your dreams of Baton Passing a single Tail Glow to Bibarel and sweeping are just a fantasy.
Found in Dream World