Actually, Unown G comes later. What happens is that a Dialga G player can Energy Gain to deafen lock, preventing a Gengar from coming into existence in the first place. Then once they have two metal energy then can replace the Energy Gain with an Unown G while continuing the Deafen Lock. Mind, this is the whole going second debacle, as a Dialga G deck going first usually ends up Calling so they can spray. I've rarely seen Dialga G players put Unown G players down on Dialga G unless they believed it was in danger of being Taken Out.
Most Dialga G decks don't really care about Shadow Room, really, especially with Bronzong, since if it looks like it'll be knocked out they just Galactic Switch and then Poke Turn to a different Dialga G. It's ungodly annoying, really.
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Are you being sarcastic?