Nice idea you have going on here, I have thought about green in my token deck. Don't have the lands for it yet tho! Do you find it works well against fast artifacts and control?
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You could use tezzerets gambit, its three mana and two life for some more poison. Maybe some more pumps to.
I like the different array of cards you have in here, I have been looking to modify my infect deck for a bit now and will be changing it from B/G to U/B. For mine I might take out two of the vatmother and put in two crusaders and maybe throne of geth with two core prowlers!