It's kind of annoying, since in my opinion the blue shield is best (their own bullets do a whole lotta damage) but I end up getting too much adrenaline, or too little if I use it once.
There's a sort of glitch for the second boss, the one with the scanner. Take your cursor out of the screen, and when you put it in again, put it in the bottom right or bottom left corner. Then you can absorb and shoot without being shot. However note that the scanner will still scan you so don't shoot when the scanner looks like it's about where you are.
Note that this is not quite as effective in the last quarter of the boss, they can still hit you.
Sigh. If you think it's too hard then too bad for you.
The only thing that annoys me is the scanner starts shooting you like mad if you even shoot. Other than that it's quite easy.
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 "Scriball"){kind=icon}
 "Dodge"){kind=icon}
 "Kongai"){kind=icon}
 "Frantic"){kind=icon}
 "Achievement Unlocked"){kind=icon}
 "Epic War 2"){kind=icon}
 "Orb Avoidance 2"){kind=icon}
 "light-Bot"){kind=icon}
 "The Necronomicon"){kind=icon}
 "Arachnophilia"){kind=icon}
 "The Last Canopy"){kind=icon}
 "Brute Wars"){kind=icon}
 "Runescape"){kind=icon}