Skill level

Skill level determines the overall difficulty of a game - how many monsters and powerups are out there, how many ammo various items give. There are 5 of them:

They are also divided into Easy, Medium and Hard. This classification determines the number of things. This means that ITYTD and HNTR will have the same number of monsters and items, but they will vary in other terms.

Early versions of Doom did not support Nightmare mode. The initial mail-order releases were version 1.1 and only included the first four skill levels. Version 1.2 added Nightmare mode support; most shareware versions of Doom distributed were version 1.2 and so included Nightmare mode.