Horde, for those who aren't familiar, is an "automated" format where a deck plays itself against you and/or your friends.  The horde deck, in this case, is composed of zombies and 60% of the deck is either 2/2 zombie (55) tokens or 5/5 zombie giant (5) tokens.  The rest is composed of an assortment of interesting zombie and zombie related cards.  Thematically I decided to keep all my zombies humanoid in nature.

The first 1-3 turns the "live" players have free to set-up.  They all share a life-total and can discuss play choices.  Their goal is to exhaust the zombie deck.  Each point of damage mills one card off the top of the horde's library.

Once the horde takes its turn things are relatively simple.  It flips the top card of the horde.  If that card is a token it continues to reveal cards until a non-token card is revealed.  Each revealed card is played immediately.  All zombies have haste and must attack each turn if able.  The horde cannot block.

If the horde has to make a decision (ie. Fleshbag Marauder) it is made randomly, when possible.  In the case of Planeswalkers on the battlefield, each creature from the horde rolls randomly to determine where it attacks (players or planeswalkers).

The horde has infinite mana (for the purposes of things like Propaganda), and any cards that end up in the horde's hand may be played at any time. 

The opposing team generally works best as 2-3 players, but can be done in any number.  The more time the humans have to setup the easier it is, but blow-outs can still happen.  EDH/Commander decks can be used too as well as standard decks.

There is no official banlist for the format, but because the horde completely folds to infinite combos they are generally discouraged, as are other cards that would simply shut down the deck entirely (it's a format purely designed for fun!)