On the second full attempt I used a pretty cheap method. Setting the reload button to auto fire so it reloads continuously and the fire button to rapid fire (when button is pressded down). This basically gave me an infinite machine gun with no reason to reload manually.
Even with all that I still lost though. I would have to learn the three bosses and practice them seperately to survive I think. Theres also easy mode to fuck with for a kill.
Strangely I could only reload sometimes and it seemed delayed when I tried to do it manually by pressing the button. Not sure if theres some timing mechanic or something Im missing with that.
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