For the red mage to stop the Engine gaining life with just burn is a minimum of nine
Green Though green is mostly associated with Humans and Werewolves on Innistrad, it's also, unfortunately, the colour of spiders, insects, and the other creeply-crawlies that stalk the forests of Kessig and Ulvenwald
In other words, while the payoff here is great, it's expensive at eight energy for a 6/6, and it's unlikely to help pay for much of that
Angel of Invention Angel of Invention is a Cube top end card that has shown as a 1- or 2-of in all sorts of builds in Modern that take advantage of it as a giant lifelinking flier
Three mana is the sweet spot here, and casting this in your first main to see if it resolves before firing off Day of Judgment is a great play
Suddenly, its in play on your side of the field