yes. solo the brutalisk with jimmy. jimmy has 500 health. run. gun. grenade if you manage. basically each time jimmy stops, the brutalisk should not hit him more than once.

by the time he's done, he should be barely alive. yes. leave him alone. marines and medic can go back to some secluded place. you can bring medic along but I'd rather not risk it.

my placement on green is that Jimmy is at a safe distance from brutalisk's 11 o'clock or so. after release, just run around towards the other end of the lab.

there are league achievements where you cant do what you're trying to do. those that isnt league, you can just play with AI

I achieved by using nuke, during ally vs oppenent, all out fighting.