Anyone? I didn't understand Forbidden's response. And how do power items really work?
The Pokerus and Macho Brace combo quadruples the EVs you get. So in your examples, Gible would be getting 8 EVs. And Dratini would get 4 in your second example. As for the Power items, on top of what you normally get, you get 4 EVs in the stat the item corresponds to. Pokerus is factored in AFTER this. Example: Your Gible has the Attack Power item and beats a Magikarp (1 Speed). Gible gets 2 Speed and 8 Attack EVs. Without Pokerus, Gible would get 1 Speed and 4 Attack.