Create the Model:

Use Blender to create a 2D model.

Export the model using Blender Source Tools.

Prepare the Addon Folder:

Create a folder for your addon in the garrysmod/addons directory.

Inside this folder, create subfolders for models, materials, and lua.

Create the Lua Script:

In the lua folder, create a file named npc_yournpcname.lua.

Edit this file with Notepad++ and define the NPC's properties, such as model, health, and behavior.

Compile the Model:

Use Crowbar to compile your model into a format that GMod can use.

Place the compiled model in the models folder of your addon.

Add Textures:

Use VTFEdit to create textures for your model.

Place the textures in the materials folder of your addon.

Test Your NPC:

Launch Garry's Mod and enable your addon.

Spawn your NPC in the game and test its behavior.