Rules:

The 3 adventurers play the game of EDH as they would normally in multiplayer except they are all against the Raid Master. The Raid Master may mulligan his/her hand for free until they get a hand they are satisfied with. However, they must stop the mulligan as soon as they have a hand with 3 lands. The Raid Master may draw up to 2 cards at the start of their every turn. The Raid Master may only have any land card in their command zone. As for the Raid Emblems themselves; the key term "PHASE" applies when the emblem is flipped face up. The ability "Event!" applies when the token is removed from the battlefield. When "Event!" is applied, the Raid Master flips cards from the top of the Event Deck until they hit a card that can be cast and cast it for free. In this case, there are 4 Event Decks, one for each Raid Emblem.

Event Deck #1:

x16 Soldier 1/1
x2 Smite the Monstrous
x2 Glorious Charge

Event Deck #2:

x15 Soldier 1/1
x5 Knight 2/2 Vigilance
x5 Bird 1/1 Flying
x2 Raise the Alarm
x2 Riot Control
x1 Deploy to the Front

Event Deck #3:

x3 Angel 3/3 Flying
x6 Knight 2/2 Vigilance
x6 Cleric 2/1
x2 Angel's Mercy
x1 Worship

Event Deck #4:

x2 Angel 4/4 Flying
x1 Rule of Law

It isn't necessary for the Raid Master to use the deck listed above, as any edh deck can be used. But the deck above is good to start with for both flavor and balance. Tweaks can be made based to the liking of your raid group. Any suggestions to mechanic fixes or balancing issues is recommended. We wanted to keep the rules simple and malleable, so that anyone with an EDH deck could participate.

Source:
Raid Format ~ Kjeldoran Outpost Siege