A strategy for level 12: move Left until you hit the wall. As soon as you hit, move Up. As soon as you hit the wall, move Right, then down, then left, then up. Move as fast as you can and you will herd the enemies into the center. Do not kill any enemies, then they will no respawn on the edges. Doing this, I finished the level with near full health, zero kills, and reduced lag by a lot. 1 minute of real time = 46 seconds game time. I was done with level 12 in 15 real minutes.
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 "Hover Bot Arena"){kind=icon}