As a biogical, you should use the Disrupt to take away the Baron's focus. It's easier if your Disrupt is upgraded. If his focus is under 15, he'll use Deep Burning, doing about 2,500 damage to himself for 3 turns.
As a Hydraulic, use Regulate.
Defeating the Baron is easiest with a Psycological. Make sure your Echoed Screams is upgraded to the Max, and you should bring a fully Implosion. Wait for the Baron's focus to drop to 15, then use Echoed Screams. Next turn, use Implosion.
1. Sacrifice each one of your mates. Each sacrifice gives you thousands of hitpoints for several turns. The baron cannot hurt you. He drains his focus trying to get at you but your health and focus keep rebounding. After that he enters deep burning.
2. When deep burning stops, use retrograde on yourself and he will be annihilated as soon as he attacks you.
I found this boss very easy. I just kept attacking him, debuffing him and I used "Wraith Form". As a psychological, get that skill as fast as you can. It's in the energy tree. Don't forget to get energy mastery. When he has 1/2 hp or so, he will cast a focus recovery spell that damages him for 2.5k each turn.