Simple

The Pokémon is prone to wild stat changes.

Doubles the number of stages gained or lost when this Pokémon's stats change.

In Black 2 and White 2, Simple doubles each stat-stage increase or decrease when it occurs, within the usual -6 to +6 limits. Existing stages are not doubled when Simple is acquired. Baton Pass and Psych Up carry or copy the stored stages; gaining Simple does not double those existing stages. This differs from Generation IV, where Simple doubled the effective stage multiplier.