Lately I've been Modding a lot and made something that has been dubbed "invisible mode"
Now, it doesn't work via mod (due to mods being client sided) it does work in hack coded format (I have proof of both)
Exactly how you do it is you find the Addy's that have to do with player dimension (or the class)
From there, set player dimension to X:0 Y:0 Z:0
You should be invisible and no1 sees you!