Let's start with this:
One of the most glaring things in this entry is:
"To exert its powerful psychic abilities, it will stay motionless for long periods of time in intense concentration to raise its capabilities to their maximum power."
Normally, you'd think this would be a superb advantage for Goku. However, given his tendency to let his enemies power to the max before finishing them, Mewtwo might have a chance.
Yet, Goku can destroy the universe a bajillion times over, so...