This is what happens when Jaeger reaches beyond his capabilities, simply by getting angry and losing control... he goes from being a lovable, chubby guy to becoming an almost unstoppable machine of destruction without knowing any enemies. and allies.....

This happened when the army was hunting them and in the process he injured his best friend.... remember the boy he saved? Thinking that he is dead, this made him angry and enter a state of frenzy. Emerging powers that he himself did not know about.