The Drillmaster is similar to the Chaos. The Drillmaster loses shield HP when hit but increases max shield anytime he uses a skill. However the Chaos loses Health but can only increase max by killing an enemy. So since the Drillmaster just needs a skill. Then the best skill to use is the Grenade. All you have to do is equip the Drillmaster and make sure it is upgraded enough to increase max shield. Then equip Grenade and max out Grenade cool down talent. Then as your playing a room, throw the Grenade even if you don't hit anyone. It will increase your shield after every skill use. And grenades cool down the fastest. So after enough skills used you can avoid being one or two shotted by snipers. But only one from an engi.