Each of the three character modes has different strengths and weaknesses: Robot Mode is the strongest, but usage depletes an "energon resistance gauge" that will prevent the character from attacking when fully depleted. Beast Mode recharges the gauge, but can only use weak melee attacks.
The three character modes have distinct advantages and disadvantages: Robot Mode is the strongest, but using it exhausts a "energon resistance gauge," which prevents attacks when full. Beast Mode replenishes the gauge, but only allows for basic melee combat.