This thread is work in progress. A proper guide will be released later because, not gonna lie, I rushed the crap outta this.

EDIT: Guide available now
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3045483595

A lot of these commands will only take a 0 or a 1 after the main code. 0 means "Off". 1 means "On".

Reflective Objects - mat_specular 0 or 1
Fullbright - mat_fullbright 0 or 1
Fix Character Eyes - r_eyesize 0
Character Eyes - r_eyes 0 or 1
Moving Character Eyes - r_eyemove 0 or 1
Draw Decals - r_drawdecals 0 or 1
Draw Model Decals - r_drawmodeldecals 0 or 1
Draw particles - r_drawparticles 0 or 1
Show Your Own Shadow - cl_drawownshadow 0 or 1
Reduce Particles - mat_reduceparticles 0 or 1
Show First-Person Weapon - r_drawviewmodel 0 or 1

World Fog - fog_override 0 or 1
View Distance Fog - fog_enable 0 or 1
Water Fog - fog_enable_water_fog 0 or 1

Water Reflections - r_WaterDrawReflection 0 or 1
Water Refractions - r_WaterDrawRefraction 0 or 1
Draw Water" - mat_drawwater" 0 or 1
Water Fog" - fog_enable_water_fog 0 or 1

Alien Blood - violence_ablood 0 or 1
Alien Gore - violence_agibs 0 or 1
Human Blood" - violence_hblood 0 or 1
Human Gore - violence_hgibs 0 or 1

Lag Compensation - sv_showlagcompensation 0 or 1
Surf Map Acceleration - sv_airaccelerate 175 for off, 10 for on
Defuse Crazy Physics - sv_crazyphysics_defuse 0 or 1
Remove Crazy Physics - sv_crazyphysics_remove 0 or 1

Invasion Mode - r_eyesize 600
Haunted Mode - r_eyesize", -500
Classic Weapon Switch - sv_defaultdeployspeed 1 for on, 4 for off
Classic Crosshair - hud_draw_fixed_reticle 0 or 1

Right Click Garry's Mod in your Steam Library, then in the little menu click Properties. In the bottom of the General Settings, you should see an empty textbox where you can input these commands into this textbox so that they'll be applied every time you play the game. But we need to make em look nice for the game to understand properly first.... when putting commands into the launch options, they should look something like this:

"+mat_depthbias_shadowmap 0.00001" "+mat_slopescaledepthbias_shadowmap 2" "+r_projectedtexture_filter 0.05" "+r_flashlightdepthres 16384"

So if we wanted... let's say Reflective Objects turned off and Character Eyes to always begin fixed. Well, we would put this in the launch options:

"+mat_specular 0" "+r_eyesize 0"