From the series Beast Wars. Reverting to Beast Mode was when either Predacons or Maximals transformed into their animals forms. In Beast Mode, they were usually able to move faster and transforming also sped up their internal repairs. Also, in the first season, reverting to Beast Mode protected them from Energon poisoning, which was what happened when they were exposed to too much raw energon.

A mode of awesomeness; A pure blank state of mind, in which you become greater (more beastly) than anything else that stands before you.

Also used when Kicking ass at black ops and someone tries to talk to you, but instead of giving them an actual convo, you just tell them "I'm in Beast-Mode right now, GET OFF MY NUTS"

An altered state of mind, most commonly achieved in the gym. Heavy weight's become lighter, more reps get performed. Beast mode is a state of heightened physical and mental capacity. Commonly associated with personal bests.

1.A state of or doing anything accessively and or aggressively; wildin' out
2.Over-do-it