Get a doctor to follow you into a fight with the Thing
To get a doctor in the same room with you during your battle with the second giant Thing, firstalk to the large garage door. Get the doctor close to the door as well. Then, tell him to not follow you anymore. Push him as close to the door as possible; and close enough to you that when you flip the switch to open the door he will not move. Before flipping the switch, tell him to follow you again. Flip the switch and when you are shown in the locked room with the second giant Thing, he should be beside you. Use him to heal you during the fight with the Thing.