Originally Posted by
Melchior
Beast mode is simply running with additional limiters off. An EVA's armor functions as restraints on the organism within, and Beast mode releases those. Furthermore, there is no data supporting Unit 13 has that mode built-in, though that might be hand-waved in this case (Mari did not go Beast with Unit 05, for example, which implies it might be a Production Model feature). Unit 13 has the standard AT Field, a dual-pilot capability, a pair of bits (not quite funnels), an extra pair of arms, and according to the opening, an S2 Engine. The pilots have never demonstrated Halo or flight capabilities, either. Berserker is unlikely without either one of their parent's in the Unit, as well.
As it is, I see one of two resolutions.
The first - Unit 13 rampages a bit, and the world decides to nuke it death. Hard to do? Yes. Possible? Also yes. Conventional weapons can get past an AT Field, it just takes a ton of power. I imagine that no one will be living on the site for a couple thousand years.
The second - The filters on the LCL fluid give out somewhere between 16-24 hours, going by the episodes with the 12th Angel. The pilots will literally choke to death in a prolonged engagement, or will have to exit the Unit in order to clear things out. In which case, observers can key in attacks.
Without Lances or another similiar being, they cannot actually initiate an Impact, so while they can tear up wherever they land, they cannot simply end human existance. Then you run into the fact that there is a limit to how far an EVA can travel in a day, and the filters for the equipment, and so I think it is safe to say that after a day or two the situation will sort itself out. Without flight, they are not pulling hit-and-runs off on more than country-wide scales.
While an EVA is capable of some autonomous action, it tends to stop after the immediate threat is gone, so there should be little worry of a continuous rampage.