If Blue Oyster Cult has played MTG during Lorwyn, their most famous song might have gone differently.
This deck has one primary purpose: battlefield dominance. Forget "Cancel" and "Snapback", destruction of threats on the battlefield is the order of the day.
This might be a Rainbow deck, but don't let that fool you: this sucker is built for rapidly gaining control of the game and getting your Commander out as quickly as possible. The Commander is none other than the Reaper King!
The Reaper King should scare the crap out of your opponents! It is a 6/6 10 CMC creature castable for 5 mana - one of each color - or two colorless for each color instead, all mixable, which gives other Scarecrows +1/+1, and DESTROYS A TARGET PERMANENT every time another Scarecrow comes into play under your control!
BABOOOM!
This deck is CHOCK FULL of mana rocks and mana-producing enchantments as well as cost-reducing cards. Mycosynth Golem almost guarantees free casting of Scarecrows, including your Reaper King repeatedly from your Command Zone.
While I could have gone with a ton of Changelings instead of Scarecrows, the Scarecrows were, for the most part, dirt cheap. Naturally, the best Scarecrow is banned from EDH, so Painter's Servant was left out. There are a couple of Clone cards in the deck, as well, plus a Xenograph. With a number of flicker cards such as Conjurer's Closet, Scarecrows can keep hitting the battlefield. If you get Sudden Disappearance late in the game, you might as well have played a boardwipe on everyone else.
"Shattergang Brothers - How quaint!" -RK
Don't worry about the graveyard. There are nearly a half-dozen ways your Scarecrows can come back with, literally, a vengeance! Roar of Reclamation can be played with devastating effect with enough Scarecrows in your graveyard - worse if Xenograph is on the battlefield - if Reaper King is out.
Fact is, though, you shouldn't be losing very many Scarecrows from the actions of your opponents, since there shouldn't be much power left on the battlefield that isn't under your control. You can blast any permanent - land, annoying artifacts and enchantments, flyers, and so forth.
The only changes I'd probably make is to get one or more cards that allows me to cast cards as if they had Flash - Shimmer Myr is a good one, as are a few others - and maybe a Glaring Spotlight. The advantage of having a Rainbow deck is that you can literally add *anything* that isn't banned. They're on my to-do list.
[UPDATE #2: This deck is now Version 2. Check it out at
http://www.mtgvault.com/mythereal/decks/edh-fear-the-reaper-v2/ ]
[UPDATE: Despite my comment of the only changes I'd make, I made a couple others - now, More Awesome! Added Kurkesh, Onakke Ancient and Strionic Resonator. One doubles my activated non-mana abilities of artifacts and the other doubles my triggered abilities, for either a Red or two colorless respectively. Unfortunately, my mana production is reduced.]
Mana ramp as soon as possible, and don't worry about getting hit early on. More than 20% of nonland permanents are 3 CMC or less! Nearly all of those are also mana ramps. It's not inconceivable that you get Reaper King out by Turn 4.
With Reaper King out, start bringing out your Scarecrows, blasting away the emerging or existing threats on the board, gaining board dominance. Try to get Xenograph out early, and/or Leonin Abunas. March of the Machines with Xenograph and your Reaper King out makes each of your noncreature artifacts Scarecrows in addition to their abilities (keep in mind Summoning Sickness - a minor side-effect of MotM).
For those of you not simply satisfied with tons of mana generation, there is an infinite mana loop combo that has the potential for allowing you to draw and cast your entire library in a single turn, and to cast your entire library and graveyard in just two turns. That means that you almost cannot lose the game, especially with 57 +60/+60 double-hexproof indestructible Scarecrows coming into an otherwise empty battlefield! At the end of your turn, discard down to seven cards in your hand.
Don't forget to discard or sacrifice Wonder to make all your creatures flying, too.