I tried the engineer out today. Her mechas can get barrier points in a variety of ways, which are useful for blocking damage before they get to health. I noticed after an early fight that when you move to a new dungeon weeks later, the barrier points are still there on any monster that still had them.

To make a long story short, using a roaster, a mechanic and an aerobot plus an artefact that grants mechas barrier points if they hit a hero that has at leave half their health, I got all the way through the first stage of the engineer's campaign without losing the first fight room once... the end stats stated I had three minions get killed in total. By the time I got to the final champion, the mechanic was sitting in front with over 700 barrier points. This seems rather broken.