Dead by Daylight Iron Will starts out as a character-specific Perk, locked to Jake Park, though persistent players will have the chance to unlock it for all characters in its basic form via the Bloodweb. Down below, you're going to find all the info you need to know about Iron Will.
What is Iron Will?
According to the game's Wiki page, Iron Will is a perk that allows Survivor characters to enter a meditative-like state to numb some amount of pain. In practical terms, what Iron Will does is that it reduces grunts of pain caused by injuries by 50 / 75 / 100%, depending on its particular level.
Iron Will will, then, allow your Survivor to be significantly more agile even during extreme duress, such as, you know, being chased by an unkillable supernatural murderer that's hell-bent on sacrificing you to an eldritch being. The usual.
You get the chance to unlock Iron Will in its basic form (50% grunt reduction) for characters other than Jake Park at level 30, which means a considerable investment of both time and resources, if you'd like to use the Perk in custom builds.