Iron Crypticle

This is one of the bosses that shows up on the first floor, can be encountered on Easy. He has a damage phase which is the only time he is vulnerable, basically when he starts shooting the sweeping laser beam, just keep going in the same direction that it's going to stay away from it while shooting Gnasher. He is still vulnerable for a good bit after the laser beam stops, then the whole cycle repeats where he's invulnerable again.