I hate the brain

So me and my friend are playing legendary mode after not touching the game since 1.3 and it took us a couple of days just to be able to fight the eye and another day just to be able to kill the eye consistently but now we are stuck on the brain and I have no clue on how I should attack this thing, I've tried grenades, jester arrows, and just never letting go of r2 with the mini shark so if anyone could explain how I can not get TWO SHOT by creepers I would be so happy

My friend is doing mage and I'm doing ranger