Rainbow Efreet can give your commander a very strong protection ability. And if your commander is going to have a bunch of awesome activated abilities, then perhaps Illusionist's Bracers can be a consideration? Also, Mairsil and Skill Borrower want the same things out of deck design so maybe the latter can play backup for the former here.
Mike gives the Ballista +1/+1 as it's not human so you need some way of killing it after you've pinged an opponent (seriously, who do so many people miss this?).
Well I can't speak for everyone else, but I missed it because I'm bad at reading cards before posting. Thanks for clarifying.
I couldn't even do the math But am I right about the doubling damage stacking, so the damage dealt would have been 5^29?
You're right about the doubling effects stacking with each other but doubling corresponds to multiplication by 2, not to multiplication by 5. So the damage would be (Zedruu's power + Thassa's power)*2^29 = 3,758,096,384. Or, if you prefer, 375-809-6384. As someone who regularly beats face with Zedruu I'm absurdly envious right now. Well done.
Naya also has a whole bunch of enchant lands which give mana abilities.
Any consideration for Sylvan Tutor or Tolaria West?
Why do you need to get Viscera Seer and Body Double before getting Mikaeus, the Unhallowed and Walking Ballista? Don't the latter two just win the game on their own?
Mirari's Wake is a notable omission.
Combat would be the most complicated thing of all time if every permanent were an artifact and every creature were Arcbound Ravager.