The boss is at level 15 and when he arrives all other enemies vanishes.
Main thing to win medium badge and killing the boss:
Shield after using active + Freeze time when hit + HP after losing last shield
After killing boss you can get upgrade that makes your combo never drop. Together with the 10% for combo-orbs you get ridiculous dmg. At level 30 my Combo reached 400x and I selfdestruct myself.
The game is bugged. Im at lev 4, last ring. The fifth blue triangle has moved sligthly and now covers both the inner and outer side, making it impossible to pass.
Since everyone is complaining on the Controls I have changed the default to not using mouse look, and AD for turning. You can turn mouse look on/off by using Q if you prefer it.
I'm sorry about the bad controls. Apparently mouse-lock is only available in full screen mode. I searched a lot to find a solution for this problem, but with no success.
Just made it to lev 62 in Endless swirl with the following easy config. Four shadowkillers with upped atk, plus one devourer with upped Hp and kickback.