Statistics Amplification is when a character raises their parameters in the middle of a fight, and this is not related to their base form or some sort of "hidden power" that has been hidden or held back.
These boosts are usually temporary and are specific to one or a number of statistics.
This also not to be confused with a change in form or state, and is thus not typically associated with any new abilities in particular. Instead, this ability serves as a means of overcoming the opponent through a sudden increase in combat effectiveness.
This ability is very common in video games but is still prevalent within other works.