Everything in this guide was done on hardcore, softcore differs from it. No hand-holding,
thats why only the names of the rooms are mentioned, not how one can get through them.

The damage upgrade (pictured below), if applied to the pistol, has the following effects:







Creeper (Weakpoint: Head)
5 Pistol rounds -> 3 Pistol rounds

Slashy (Weakpoint: Head)
3 Pistol rounds -> 2 Pistol rounds

Boomy (Weakpoint: Abdomen)
2 Pistol rounds -> 1 Pistol round

Burgerman (Weakpoint: Head)
8 Pistol rounds -> 5 Pistol rounds

This upgrade helps with the "Oldschool" achievement (beat the game using only the pistol).

Quarantine -> Storage -> Start -> Crouch -> Climb -> Jump Up -> Shimmy -> Jump Back -> Complex -> Climb Down -> Gateway -> Item [take & place Plug] -> No Item -> Item (Vent) [remove Plug] -> No Item (Vent) [place Plug] -> Junction (Case: Green Keycard) + (4x Floppy Disks) -> Lock [use Green Keycard] -> Lockpick (Lockpick [bruh]) -> Lock (unlock Case: Yellow Keycard) -> Junction [remove Plug] -> No Item -> Item (Vent) -> Gateway [place Plug] -> Green Key [use Yellow Keycard] (Supply: Green Keycard) -> Gateway [remove Plug] -> Item [place Plug] -> No Item -> Way Down (Vent) -> ? (Vent) -> Lock (Vent) [use Green Keycard] + [take Red Keycard] -> Junction -> Connector [use Red Keycard] + [use Manual Override & take Jack] -> Way Down [press Button] -> No Item (Vent) [place Jack] -> Item (Vent) [remove Plug] -> No Item (Vent) -> Way Down (Vent) -> Connector) -> Stairs -> Pool [take Mine + 2x Floppy Disks] -> Stairs/Security Post [place Mine + use Manual Override & take Pistol + Supply: 1x Pistol Round] -> Pool -> Shaft [take Screwdriver] -> Stairs (Vent) -> Pool [shoot Mine & use Screwdriver] -> ? (Vent) [take 2x Floppy Disks + Supply: 20x Pistol Rounds] -> Pool (Vent) -> Stairs -> Connector -> Way Down -> No Item (Vent) [use Screwdriver] -> Jammer (Vent) [remove Jammer] -> Battery [place Plug + dodge the enemy & use Screwdriver] -> Pipes (Vent) (Supply: Medkit) [open Doors] -> Way Down -> Connector -> End/Test End [place Jammer] -> Checkpoint [store Screwdriver] -> Hall -> Central Hub

Administrative/Checkpoint -> Alley (Haydee: 10x Pistol Rounds) -> Dining Room (2x Haydee: 5x Pistol Rounds) [take Pliers & disarm Mines to take them as well] -> Alley -> Checkpoint -> Central Hub

Technical/Connector -> Hall -> Stairs (Haydee: 10x Pistol Rounds) -> Power Pipes Control/Transfer Hall -> Maintenance (Haydee: 5x Pistol Rounds) -> ? -> Hall (Vent) -> Checkpoint [take Screwdriver] -> Hall -> Central Hub

Technical/Connector -> Hall -> Stairs -> Power Pipes Control/Transfer Hall -> Elevators/Hall -> Elevator Control [pull the breaker] -> Monitoring (Haydee: 10 Pistol Rounds) -> Supervisor (Vent) [take Plug] -> Transfer Hall -> Utility [place Plug into blue] -> Transfer Hall -> Maintenance (Haydee: Component B + Haydee: 2x Floppy Disks) -> Relay Hall (2x 5x Pistol Rounds) [turn Green Line right] -> Relays [turn Green Line up]-> Relay Hall -> Main Gate/Relays -> Main Gate [take Power Card] + [turn Blue Line up)-> Relay Hall/Relays -> Relay Hall -> Supply -> ? (Vent) (Haydee: 10x Pistol Rounds) -> Supply (Vent) [use Manual Override] -> Transfer Hall -> Utility [switch Plug to green] -> Transfer Hall -> Stairs -> Level 2 Hall -> Restricted (Haydee: 10x Pistol Rounds) [turn Red Line right -> Technical Hub -> Lavatory -> Binary (2x Mine) -> Offices -> Dispatch (Mine + 2 Floppy Disks + Component A) -> Technical Hub -> Entrance/Restricted -> Duty Room (Haydee: 10x Pistol Rounds) [take the Bolt cutter & use Manual Override] -> Restricted -> Hall -> Connector -> Central Hub

Medical -> Checkpoint [store Bolt cutter] -> Obstacle Course [take Bolt cutter] -> Test End [take Jammer] -> Connector -> Way Down -> Pipes [optional: Shotgun] -> Battery (Vent) [remove Plug] -> Jammer [place Jammer] -> No Item (Vent) -> Way Down (Vent) -> Pipes -> Shortcut -> Storage (Vent) -> Quarantine [use Bolt cutter & use Manual Override] -> Hall (Haydee: 5x Pistol Rounds -> Central Hub -> Technical -> Hall -> Stairs -> Power Pipes Control/Transfer Hall -> Utility [remove Plug] -> Transfer Hall -> Stairs -> Level 2 Hall -> Connector -> Central Hub

Engineering (10x Pistol Rounds) -> Hall -> Stairs -> Level B -> Elevator L [place 2x Plug] -> Level C (Haydee: 10x Pistol Rounds) [call the elevator] -> Stairs -> Level B -> Elevator L [take Plug] -> Level G [call the elevator -> Elevator L [take Plug] -> Transit: A -> Substation (Haydee: 10x Pistol Rounds) -> (Mine + Haydee: 5 Pistol Rounds) -> Control -> ? (Vent) (Haydee: 5x Pistol Rounds + Haydee: Medkit) -> Utility (Vent) (2x Haydee: 5x Pistol Rounds) [take Wrench] -> Hall [use Manual Override] -> Transit -> Level G [place Plug] -> Stairs (Haydee: 5x Pistol Rounds) -> Level C -> Elevator L [take Plug] -> Stairs -> Entrance -> Central Hub -> Central Hub

Medical -> Hall (optional: -> Storage [Haydee: 10x Pistol Rounds] -> Utilities -> Registration (Haydee: 10x Pistol Rounds) -> North Wing (Component C + 2x Floppy Disks) -> North Wing (Haydee: 10x Pistol Rounds) -> Surgery (Haydee: Medkit) [take & apply Damage Upgrade]

If my notes are correct, I've ended up with 172 out of 190 Pistol rounds spent. I've also used 9 out of 10 mines. Feel free to improve on this with dodging enemies, clever use of the exploding ones or more efficient mine placement. I may or may not enhance this guide over time with pictures and may even cover optional parts (e. g. getting the Shotgun).