Doomguy has a couple of mechanics exclusive to him.

Ammo

Most of Doomguy's weapons require ammo. You can replenish your ammo by purchasing interactables.

Bandolier pickups will replenish 20% of your ammo, and hitting boss enemies with the chainsaw will replenish 5%.

Weapon Switching

Doomguy doesn't use skills like most survivors. Instead, switch your active weapon using the number keys.

1 - Chainsaw

2 - Super Shotgun

3 - Chaingun

4 - Rocket Launcher

5 - Plasma Rifle

6 - BFG-9000

Doomguy is able to use some of the cheat codes from DOOM 2.

iddqd - toggles godmode

iddt - triggers radar scanner effect

idchoppers - switches you to the chainsaw and gives 1 frame of invincibility

idkfa - full restores your ammo