I strongly suggest you join our Discord, all the info from here wouldn't be possible without all the work from there. Also is the best place to ask for help for modding!

The mods pics used here are also from there, credits to Azure, polar, Zai_ and me.

1. Install mods

This is the simplest one, naturally, simply get Unverum, and use it to download/install mods.
If you're not sure about how to do it, check this guide :
Unverum Installation Guide

1.1. Troubleshooting :

1.1.1. "Steam asks me about a command "RED" when launching the game"

Make sure you changed "executable" for "Steam" in Unverum.

1.1.2. "The mods I downloaded aren't showing up"

Make sure you have them enabled and they don't replace the same files.

1.1.3. "I installed .NET but it keeps asking me to install it."

Make sure you installed the desktop apps x64 one.

1.1.4. "I installed a skin mod but it replaced all slots."

This happens when a mod creator doesn't bother to give separate downloads for each slot, and instead put them all in a big single download.

To fix this, you can right click the mod, then press "Open Mod Folder".

And once you are there, simply delete all the .paks/sigs you don't need. If you only want the mod in, for example, Color 05, then only keep that one and delete the rest.

2. Make Texture Mods

Before you start, I HIGHLY recommend you read this to understand how textures work exactly in Strive, it will help you make better mods :
Guilty Gear -Strive- Texture Breakdown

And here are some guides for Strive texture modding :
UE4 Written Texture Modding Tutorial
Modding Strive 2.0
Ultima's video tutorial

Other helpful resources are :
Characters ID List
Characters Texture Maps (You have to be in the modding Discord)
Strive UE4 Material Recreation
C&A ASW Tools and its guide

2.1. Troubleshooting :

2.1.1. "My character is completely or partially blue"

This means you got your files from NameOfYourProject/Content instead of NameOfYourProject/Saved/Cooked/WindowsNoEditor/NameOfYourProject/Content

Another possible issue is you having a mistake in the path inside of UE4; Like for example, having 2 "Content" folders instead of just one.

2.1.2. "My mod is not showing"

This most likely means your UnrealPak path is wrong somewhere, for characters it should be

RED/Content/Chara/XXX/Costume01/ColorXX with your textures inside
(XXX being the ID of your character and XX the color you picked)

The usual mistakes people make here are; "Costume1" instead of "Costume01", "Color1" instead of "Color01", "GGT" instead of the ID of their character, etc

2.1.3. "My colors look too dark"

You most likely forgot to uncheck sRGB inside of Unreal Engine 4 before cooking, or didn't save afterwards.

2.1.4. "Part of the texture doesn't show up when I open it in Gimp/Paint.net/etc"

Stop using that and use Photoshop instead. If you SERIOUSLY don't want to download Photoshop for whatever reason, use Photopea instead, is almost as good.

2.1.5. "There's a weird gradient over my texture in-game"

Read the Sss alpha section of the texture breakdown.

3. Make Text Mods

You can check the guide here :
Guilty Gear Strive Text Modding Guide

4. Make 3D Mesh Mods

Okay so I will start with an advice for beginners;
DON'T try 3D modding not knowing shit about Blender/3Ds Max.
First get familiar with the program, do some low poly models, a simple rig, simple textures, get the basics of what unwrapping/UVs are, etc etc
If you try to go modding blind you will be stuck like a dumbass in the simplest things... I can tell you this because I lived it. :^)

Now, about the actual process, you can find a video about it here :
GuiltyGearStrive - Mesh Modding ProcessFlow
GuiltyGearStrive - Mesh Modding Tutorial (beginner)
GGS - Mesh Modding Guide

If you want to know more about how Arcsys models work, I strongly suggest checking this video :
GuiltyGearXrd's Art Style : The X Factor Between 2D and 3D

To preview your 3D mesh inside of your software of preference you can use one of the following shaders made for each one :
Strive ShaderFX (3Ds Max/Maya)
Arc System Works Shader (Blender)
Strive UE4 Material Recreation (Unreal Engine 4)

And to make real scalable outlines like the real game check this guide :
GGST Outline Tutorial

5. Make Characters Animations Mods

Okay so, this one is a bit tricky.

We can import animations, but we can't export them properly; Let me go a bit more in detail.

Currently umodel, the program we use for exporting, doesn't export the scaling changes in animations.
This might not sound pretty important at first glance, but Arcsys actually uses it a lot in ALL their animations, even those that don't seem to have anything fancy going on.
In the regular battle animations (the not cinematics ones) they use the scaling to fake depth/perspective, and they make the hands/feet bigger to make them more visible; That stuff is lost when exporting with umodel.

If anyone can or knows of someone who could potentially fix this issue in umodel and allow for animation exports with scaling, please let me know, I'm even down to pay if needed.

That aside, animations imports work as expected like most UE4 games, sometimes you might face a broken mess because of animation bone index discrepancies between your imported skeleton and the original one from the game but that can be easily fixed with this guide.

6. Make Stage Mods

To do stage stuff I strongly suggest you have a basic idea of how to put together levels in UE4

Stages can be found in Map/Battle/
As to how to modify them, you can import your own umaps over the BG1, BG2 or BG3 stage files.
DON'T replace PL, BG0 or EFF, those 3 contain important things for the stages that are better left untouched.

The only limitation currently is that we HAVE to use existing materials from the game (instances can be made)
Stages is in this game use a mix of hand painted shadows in textures, actual lighting shadow and then baked/built shadows in UE4.
Kind of a weird mix but that's how it is.
My personal suggestion is to avoid building the light because that causes the characters shadows to dissapear.

I'm working on a UE4 project with assets of all the in-game stages so people can simply drag and drop existing stuff to create their scenes (like in the pic), but that might take a while.

Useful resources :
Stages ID List

7. Make Audio mods

Audio mods are as simple as textures, you can find an explanation of how to make them here :
Iiirects' video tutorial
Ultima's video tutorial

Characters voices can be found in
Chara/XXX/Common/Audio
While the background songs can be found in
Audio/BGM

Other helpful resources :
Audio Ripping Tool (See video guides for how-to use)
BGM ID list
Ultima's cue tutorial

7.1. Troubleshooting :

7.1.1. "My audio has clipping"

This can be sometimes caused by using a .ogg format file.
Try using a .wav instead and see if that fixes it.

8. Make Moveset/Script mods

Guitly Gear -Strive- uses BBScript for movesets, a propietary script format made by Arcsys that they have been using since the Blazblue games.

You can find the moveset files in :
Chara/XXX/Common/Data/BBS_XXX

There are also "COL" files which store hitboxes, and "BBS_XXXEF" files which store effects related things.

In order to open the BBScript files you will need :
- The unpacker (in order to pack and unpack the moveset files)
- The parser (to conver them to readable format, and back)

You can find a full on guide here :
Guilty Gear Strive Script Modding Guide

And documentation about BBScript here :
BBScript General Documentation (Strive)
BBScript Functions Documentation (Strive)