Nightmare Walkthrough with 100% kills and secrets

A full walkthrough of Quake, including secret maps, played on Nightmare difficulty with 100% kills and secrets.

Introduction

Due to a bug in Quake, each Rotfish enemy will count twice towards the enemy total but will only increase the total amount killed by one.
Likewise, there is also a missing trigger in E2M4 - The Ebon Fortress, which prevents 4 enemy Scrag from spawning in a player accessible area when playing in Hard or Nightmare difficulties.

The videos for maps affected by these problems were run with a modification that fixes the enemy count at the level intermission.

E1M1 - The Slipgate Complex

E1M2 - Castle of the Damned

E1M3 - The Necropolis

E1M4 - The Grisly Grotto (leads to E1M8)

E1M5 - Gloom Keep

E1M6 - The Door to Chthon

E1M7 - The House of Chthon

E1M8 - Ziggurat Vertigo (secret map)

E2M1 - The Installation

E2M2 - The Ogre Citadel

E2M3 - The Crypt of Decay (leads to E2M7)

E2M4 - The Ebon Fortress

E2M5 - The Wizard's Manse

E2M6 - The Dismal Oubliette

E2M7 - The Underearth (secret map)

E3M1 - Termination Central

E3M2 - The Vaults of Zin

E3M3 - The Tomb of Terror

E3M4 - Satan's Dark Delight (leads to E3M7)

E3M5 - The Wind Tunnels

E3M6 - Chambers of Torment

E3M7 - The Haunted Halls (secret map)

E4M1 - The Sewage System

E4M2 - The Tower of Despair

E4M3 - The Elder God Shrine

E4M4 - The Palace of Hate

E4M5 - Hell's Atrium (leads to E4M8)

E4M6 - The Pain Maze

E4M7 - Azure Agony

E4M8 - The Nameless City (secret map)

End - Shub-Niggurath's Pit