Updated! A few major changes: Ludvics Test Subject didn't make the cut. out of 10 test games, I only was able to max him out once, and he didnt help me win at all. Still combo'd off and won with a Devils play. Also, as a 0/3, he's got pretty poor defensive stats, so I'm disinclined to block with him. An extra Fog Bank took his place. Also, the difference between 4 and 5 toughness was relevant more often than I had originally thought, so I gently cut the number of Doorkeepers down to 1. He functions as the decks third win condition, and Murmuring Phantasam serves as another durable wall in its place. Haunted Guardian is super strong vs quick green and red decks, but is mediocre vs white (lots of opposing first/ double strikers, and is similarly weaker than my other walls vs black and blue. Still a great choice for the deck, and I'm considering an additional few in the sideboard. Now, for the key difference between 9000 and 9001. Everything instant or sorcery in 9001 has Flashback. The deck only needs to reach infinite mana, and then the combo begins. Because Gatecreeper Vine helps thin the deck out, using a Trackers Instinct or Forbidden Alchemy both put 8 cards in my graveyard, which, except in very rare cases, nets me another Trackers Instinct or Forbidden Alchemy. Rinse and repeat. We still have another 22 million in the mana pool to burn. I can deck myself, and in the process, discover the win-condition. It's a much more streamlined, compact, and reliable combo deck than the first one was. 

Why only 3 Fog Banks? They don't die to combat; extraordinarily helpful in getting to 4 living breathing Defenders. You should run 4. Flying is icing.

And two genuine questions here:

1. Have you noticed the difference in 4 to 5 toughness mattering a lot?

Reason: If 4 toughness is effectively just as good as 5 against the creatures you face, you can use Doorkeeper instead of Murmuring Phantasm to have another card that kills (provided a 2nd Galvanic Alchemist, which isn't unrealistic).

2. Why Urban Evolution? It doesn't seem like you're ramping to anything in particular. So is it just to draw 3 cards? Of course, drawing 3 cards isn't bad, but I'm thinking with this deck's particular properties tutoring would be more useful - most likely in the form of Forbidden Alchemy, or more Increasing Ambition.

And a playtesting question. How do the Haunted Guardians perform?