I like the changes. Looks pretty good. My only thing is that the Voltaic Key really doesn't do you much good. It's a speedbump. Yes, it untaps the Liquimetal or the Vat, but it's not really amazing. I would like to see 4 more basics. That will put you to 24 land, which helps to never miss a land drop, so your Horde-Smelter comes out on time. Other than that, I think you're ready to demolish some FNM's.
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So, this reminds me of a green deck i built with the same theory in mind. It used the Liquimetal coating to turn almost everything into artifacts, and then blow everything up. It was pretty swift. Main differences though, was colors - obviously - and choice of spells and methods. My deck got a pretty good lockdown with Sylvok Replica and Mimic Vat. With a liquimetal, you continue to blow things up for 4 mana each turn. Also, my deck was chock full of Naturalize, Nature's Claim, Acidic Slime, and the new Viridian Corruptor. You definately have some strength with Horde-Smelter, but i'm not sure it's enough... splash some green to really up the hate. You would pick up so many more lethal spells, and it's really easy to do given the amount of dual colored lands that are available... Another cool thing about what i did was run Ancient Stirrings... 1 green mana, check the top few cards, snag liquimetal or mimic vat, or sylvok... at the worst, you grab a land! I would strongly suggest splashing green for the stirrings, and, to be honest, green naturally has more artifact hate. Another neat trick i had was Ezuri's Brigade, because with liquimetal and any other artiface in the deck, i had Metalcraft... and an 8/8 trample on a Mimic Vat is nasty... Just some ideas.