the list looks pretty solid for Tempered Steel, though I've seen a lot of lists also run the blue splash for Master of Etherium. You can use Glimmervoids for the blue splash, or play Hallowed Fountain as well. It also gives access to Thoughtcast, which is needed in Affinity-type decks which vomit their hand by Turn 3. Can also play Black for Disciple/Ravager Backup plan, and also gives access to backup kill spells.
Missing Paths as well. Those are my only things to add to it. May not hold up well against combo decks without a blue splash, because with that you can add Spell Peirce and Rune Snag, etc.
I played a similar deck in Extended at a PTQ last season. It was Esper Tezz Tempered that actually did pretty well. Tezzeret and a Ranger of Eos can be huge finishers on turns 4 and 5 with a Tempered on the field.
4 Memnite
4 Ornithopter
4 Court Homunculus
4 Steel Overseer
3 Tidehollow Sculler
2 Etched Champion
2 Ranger of Eos
Non-creatures (15)
3 Mox Opal
4 Cranial Plating
4 Tempered Steel
4 Dispatch
5 Plains
1 Swamp
4 Marsh Flats
4 Flagstones of Trokair
4 Godless Shrine
4 Darksteel Citadel
4 Thoughtseize
2 Inquisition of Kozilek
3 Surgical Extraction
4 Ethersworn Canonist
2 Etched Champion
Without most of the artifact lands, tempered steel might be a better choice than affinity. Is this deck going to be able to compete?
Missing Paths as well. Those are my only things to add to it. May not hold up well against combo decks without a blue splash, because with that you can add Spell Peirce and Rune Snag, etc.
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http://forums.mtgsalvation.com/showthread.php?p=8122582#post8122582