I think your best option relies in pitting everyone against yellow. Work something out with your partner, green, to give blue central america by pulling back his troops to venezuela next turn, and then cash in your set. Place all your troops on scandinavia, and force him out of iceland, rather decisively. Then, make him a deal (or rather force him into one): he can either accept your offer, take central america, hold north america, get his continent bonus, and join in on attacking yellow with you and green, or he can attempt to kill you, which he can not do with merely 15 additional troop, and face certain death at the hands of green and an ever expanding yellow. Your (hopefully large) standing army in iceland should force him to take your deal. Then move some troops to Ukraine, and wait for blue and green to set up North America (while they do that, work on whittling down a nearby yellow country, probably Afghanistan, probably even take it over - just make sure you do not come across as too imminent a threat). Then, work with blue and green to take asia - task blue with the upper countries, which he is closest too, and green with the lower. You will cut through the middle - but do so quickly (this is why taking Afghanistan beforehand or something might be a good idea), so you are the only one poised to invade Australia (maybe work with green to whittle Siam first, or just simply amass troops prior to so it does not matter - remember, you have the most prep time. Blue and green had to work out NA first). Once you have done so, maybe stall a bit to ensure you kill yellow and collect his cards. Once done, turn on blue, who likely harbors some ill wills for being basically coerced into the deal (which is now over), and pincer him with green. With your card and continent advantage, you should be able to ensure you come out on top of the conflict over green, so that when the final showdown comes, you are ready. The method outlined here seems to me to be the best, as your reputations stays in place (no deal breaking) and you have sufficient chances to pull off a win (or revise plans if things go wrong - if you cannot take out yellow, maybe you can work it out so green and blue kill each other in a struggle for Asia and Australia). Please critic, if at all possible.