With conservative play and some skill, you could beat Doom on the hardest difficulty without dying once.

Someone beat Doom on the hardest difficulty without dying

The highest difficulty level in Doom is called Ultra Nightmare. As the name suggests, this one is not for the faint of heart.

If you remember, this is the difficulty setting even developer id Software couldn't beat, doing it without dying is astonishing.

Here's YouTube user Zero Master's full attempt, clocking in at just below five hours. Although you can't call his skills into question, he does play somewhat conservatively in some parts.