That One Boss : Every boss has the ability to become this when obtaining when trying to obtain the titles, since to obtain them you can't take a single point of damage when fighting them.
In normal gameplayThe Bear and Evans especially since both have instant kill moves if you are too slow to react.
Banks due to his unpredictability while battling him, he uses turrets, a machine gun, grenades as well as a move where he grabs you and if you don't shake him of fast enough you will lose a lot of health - which is a problem since depending on your skill level in this game, may have used most of your healing resources while trying to reach him.
That One Level : Nearly every single driving mission can and will make you pull out your hair.
The Escort Mission since you have to go backwards and forwards throughout the level traversing through ash and poison gas and carrying Iris makes you move more slowly than normal so if you screw up you die. Some point in the level Iris goes missing and then you fight The Bear.