a summoned barrier of ice  

ok, I have planted the bugs, gotten accross the chasm with the crafty use of the 3 boards. Scaled the wall, got accross the gap and got the board on the other side. I, to this point think Im being pretty ingenious. But this #$%^ summoned barrier of ice is killin me! Targetable but unattackable. Not destroyable. Please dont tell me I have to kill this yellow ^^^ heroic solo to get the key to that dang keep! Because we all know that isnt going to happen. All advise appreciated!

Thanks!