Mon-Green Elves (Devotion)
Devotion + Elves = Fast and over powered. This deck usually wins by the 3rd via Huge trample creatures. Ramp up combos are Arbor Elf/Utopia Sprawl and Nykthos, Shrine to Nyx/Garruk Wildspeaker.
Turn 3 win
Turn 1: Drop Forest for Arbor Elf.
Turn 2: Drop Forest for Utopia Sprawl on untapped Forest. Tap enchanted Forest 2 mana and use Arbor Elf to untap it, than tap it again for a total of 4 mana. Cast Garruk Wildspeaker and use his +1 ability untapping your lands, than tap them again for 3 mana to cast Burning-Tree Emissary and Champion of Lambholt.
Turn 3: Drop Nykthos, Shrine to Nyx and tap your enchanted Forest for 2. Use the 2 mana to tap Nykthos, Shrine to Nyx giving you 8 mana. Use 7 of that to cast Regal Force, draw 4 cards, than use +1 ability on Garruk Wildspeaker to untap your tapped lands. With the 1 floating in your mana pool and your Forest to use Nykthos, Shrine to Nyx adding 11 mana to your mana pool. Use Arbor Elf to untap your enchanted Forest. Tap both Forest for 3 for a total of 14 mana. Cast Genesis Wave for 11. You will almost certainly drop a Craterhoof Behemoth "the later in this process, the better". You have Burning-Tree Emissary, Champion of Lambholt and Craterhoof Behemoth(s) as attackers this turn. Even if Craterhoof Behemoth was the first one to drop with Genesis Wave you still had 5 creatures out at that point which means you can swing for 30+ trample damage. What's more likely is Craterhoof Behemoth comes out after a few other creatures giving him and your other creatures even more power. So chances are you will be swinging with well over 30 trample damage.
Game Over!
Turn 3 Win
Turn 1: Drop Forest for Arbor Elf.
Turn 2: Drop Forest for Utopia Sprawl on untapped Forest. Tap enchanted Forest 2 mana and use Arbor Elf to untap it, than tap it again for a total of 4 mana. Cast Garruk Wildspeaker and use his +1 ability untapping your lands, than tap them again for 3 mana to cast Burning-Tree Emissary and Champion of Lambholt.
Turn 3: Drop Nykthos, Shrine to Nyx and tap your enchanted Forest for 2. Use the 2 mana to tap Nykthos, Shrine to Nyx giving you 8 mana. Use 7 of that to cast Regal Force, draw 4 cards, than use +1 ability on Garruk Wildspeaker to untap your tapped lands. Use the 1 floating in your mana pool and your Forest to tap Nykthos, Shrine to Nyx adding 11 mana to your mana pool. Use Arbor Elf to untap your enchanted Forest. Tap both Forest for 3 for a total of 14 mana. Cast Craterhoof Behemoth and any other creatures in your hand Attack with him, Burning-Tree Emissary, and Champion of Lambholt for a total of "at least" 26 trample damage.
Game Over!
You at very least want 2 lands and an Arbor Elf in your opening hand. There are other 3rd kill conditions provided you draw Utopia Sprawl. If you don't have and or draw a Utopia Sprawl than the same mechanics can be accomplished on turn 4. Give it some play testing and let me know what you think. Have fun!