First this is not going to be formal because I don"t even need this plugin, I would 100% use it nonstop and love it so much. Also others would probably dowload it too. Okay I am wondering if this is possible with our a client, I don't care for telling everyone to download a client so here goes. In mob disguise you can disguise as people with capes such as notch, so would it possible to make a plugin that does a lets say multiple disguise where it uses notches cape but will disguise your skin overtop of his? I feel like this may be possible somehow by a expirienced developer.
There is a similar mod that allows capes to be seen in multilayer. however it is not a plugin. Link Link 2
With a change to the client, yes, this would be possible. Without it the client will always read cloaks from the Mojang server by username.
Well I'm going to be honest I bet their is someway to make this possible, people said vanishing wasn't possible and it was. I saw a guy who made a plugin that took away names on multiplayer with a plugin, I imagine there is some way. With some extreme knowledge and messing around.
Nope, because the server sends information about other players. The skin and cloak is gathered by the client directly from the Mojang storage servers.