Help me create a special effect for my avatar

I’m creating my vrchat avatar that I want to have a mode where it becomes partly transparent and displays a potentially animated texture behind and only viewable through it.
But because of my lack of experience with unity I don’t even know where to start.
Also we need to keep in mind that map geometry, other players, and grabbables might go in between the texture and my avatar, in addition to that we also need to consider the multiple angles it can be viewed from.
The effect I’m trying to make is a Cosmic Garro (idk how to spell it) look I have an idea of how it can be done but have no idea how to put it in unity:
By displaying an image that appears as if it is always facing the camera looking at it, in the avatar, and always displayed behind it.

Write a shader that will blend between the regular texture and the desired image. Map the desired image’s UV to screen-space to have it always face the camera. You can read the target and destination depth information to help you blend world/props/other-avatars properly between your avatar and the texture. I believe this will allow you to accomplish what I think you want, and should work reasonably well with everything else.

This is not a particularly simple shader to write.

I don’t know enough about unity to know how to do that alone, can you or someone link some tutorials that when put together can help me write this because creating this avatar is the first and (maybe) only time I’m going to use unity.

sorry if your expecting me to know more but I couldn’t find any less advanced help forums

What you want is a very specific effect. It’s unlikely there’s a tutorial to make that exact thing.

Google for Unity shader tutorials and start practicing them. It doesn’t really matter which one you start with. Once you start to get a handle on that, you will start to get some ideas on how you can accomplish the desired effect.