To my best knowledge, there is no info on how to beat him on the forum, so here we go.

I'm still not sure about some things, so please correct me...

You can not target him directly. Every time one of the barrels take damage, the squidballs appear. So be carefull with using skills that draw out too much of them at once. Lure them near the miner and make them explode and he will take damage. Do not come to close to him, as he can insta-kill players. Try to get a few engineers in your party, so they can revive eachother. Have them spam empathy.