It has no drawbacks whatsoever! It is just one of the most awesome commons in standard, I think it deservs a mythic spot right away.
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I think it is the biggest sleeper common in Besieged right now, I don't know why people have not seen it before :S
I really like the idea of Hexplate Golem as a kind of finisher, it is something that your opponent never expects so I think that when Hexplate Golem resolves it is pretty much gg ^^