Fullscreen, as already stated MAAAAAAAAAANY times, require a hacked client.
A proxy manipulate the network communication of the game.
There is NO WAY it can modify the view distance.
Proxy can Block things by do not send the packet he receive to the client(antidebug, lag and so on) or send new packets to the client to make the client use a feature WHICH ALREADY EXISTS, but in a different way.
Ex : the Hp/Loot Notification use the same in-game function which display the "Quest Completed" message.
There is no such Fullscreen function unless we hack the CLIENT.
Anti-debuff is partially done in clients. Other anti-debuff by the proxy/client, afaik, lead to d/c.
I hope this may help you to understand guys
