A Last-ditch Move
Therefore, I present to you:
Bombazar, Dragon of Destiny!
The mixing of civilizations isn't too bad, especially when you consider that they've only come up with five combos so far. Anyway, Bombazar has a high mana cost, but his power almost equals it. And like many of the cards from Shockwaves and beyond, he is put into the Battle Zone tapped, meaning that he is just asking for attacks from your opponent's larger creatures. Still, if you have Blockers, it's really worth it to have him in play. First of all, when he is first played, all of the other creatures with 6000 power that hope to tie with him are destroyed. This unfortunately includes your own, so make sure your creatures do not have this power at all costs. Then, you get another turn after that one is completed, but if you don't win at the end of that turn, you lose.
However, that means you don't need worry about losing, if you have the right stuff. Bombazar himself has Speed Attacker and Double Breaker right off the bat, so after his initial turn of being tapped, he can break all of your opponent's shields in two turns. So you should attack with your creatures, save one, to destroy all of your opponent's Blockers before Bombazar can do his job. Then, once all the shields are cleared, just attack with your last, weakest creature, and you win! Simple as that.
Of course, you need a deck with at least Fire and Nature stuff in it to even pull this off, and some Blockers from other civilizations are needed just to protect Bombazar. Once you've assembled enough big creatures (or maybe spells) to clear the enemy Blockers out, though, you're all set.
Ballom's Rating: 5/5! I've never tried this all-or-nothing strategy myself, but it sounds mighty fun! Plus, Bombazar seems like a good creature overall, even if he can lead to suicide if you're unprepared.