Section 1: What is a level mod?

In order to untangle the mess that is teaching the pre-requisite knowledge of being able to create level mods on your own, it is best to lay down the process step by step.

This is something I've noticed this wiki does not do. It may have a lot of useful documentation such as eventcalls and miscellaneous entities, but they do not put together a concise tutorial on how to use them properly.

This guide sets out to correct this.

First, a brief write-up of what exactly level mods are and how they work.

A single level in Doom Eternal has the sum total of its assets and files located within its RESOURCES files, with the file extension ".resources". You can even see them for yourself, on the Steam/Windows version of Doom Eternal for example, the RESOURCES files for the World Spear for example are located in:

C:\Program Files (x86)\Steam\steamapps\common\DOOMEternal\base\game\dlc2\e5m1_spear

These RESOURCES files, when combined, have everything the level needs to function properly. They have everything from particle effects to models to, most importantly, the file that determines how the level operates when loaded.

This file, with the file extension .entities, is what id Software themselves edit when they push a new master level out.

So all in all, these RESOURCES files are pretty important then. The only thing they don't have is the level geometry itself.