Needs more Chromanticore.
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Instead of Reverberate, why not use Increasing Vengeance? Same thing, except it has a flashback.
Edit: Keep the Unnatural Predation to. Forgot to mention that. :D
I would suggest 4 Ulvenwald Trackers in exchange for your Mirran Mettle. When you use Ulvenwald's tap effect on one of your guys, not only can you seriously weaken an opponent's potential blockers but you can increase your attacker's power as well. (Assuming that Wild Defiance is out) Also, don't be afraid to run some Miracles. Example: Blessing of Nature would be perfect for you, because you can target more then one of your creatures in the same turn, causing Wild Defiance to boost them even more. Plus if you had maybe 2 thrumming birds, you could potentially proliferate not only poison counters, but your own creature's +1 counters as well. Last thing: Way to many beef spells. I understand that beefing Infect with Wild Defiance is a great way for a quick win, but in order to beef you need creatures. Which you currently only have eight. I'd get rid of all your spells, except for your Mutagenic Growths and your Artful Dodges and replace them with some creatures and a few beef miracles (No more then 4). Hope this helps your deck!