Shared Library/Shared Graveyard Singleton
Begin with 90 (or 250) nonland magic cards, double faced cards may be included, but it's not recommended. Grab 2 other people for the intended multiplayer experience. Shuffle that pile of cards into one stack of cards. This is our library now comrade! ;P
Each player draws a hand of 7 cards. Use the "partial paris" mulligan, if any mulligan at all, or just start the game!
Each player's life total becomes 25.
Once during your main phases (when the stack is empty), you may play one card face down, that's now your land that's taps for any one color of mana. It's like morph, it doesn't have a name, but, unlike a morph, it's a special action that doesn't use the stack and can't be responded to. Like a land. You should keep track of them like any other face down permanents, not shell game them around and stuff... You can look at face down cards played as a land any time. Well, as long as you control it.
If you blink a land this way, you have luck, of it's a permanent, it will be face up now! Otherwise it goes to the graveyard. Speaking of which: The graveyard is also shared!
Rulings (trying to sound like rules text)
If multiple cards are put into the graveyard, the active player chooses in which order their are actually put into the graveyard. If this cards have multiple controllers it goes in Active Player Non Active Player order, into the graveyard. To clarify this, the active player decides first in which order the cards they control are put into the graveyard zone, then the next player in turn other does so, and so on. This also applies to milling/dredge.
The owner of a permanent is the player under whose control it came onto the battlefield.
If the permanent changes control afterwards, keep track of it's original controller, it's that permanent's owner.
The owner of a card in the library is every player, still in the game.
If an effect says that you can select "a player" can target yourself. If it instructs you to choose "an oppent" you must do so. Same is true for targeting.
If a player leaves the game, all permanents they own are exiled. The same is true for the hand cards.
The rest of the game functions as "normal" (hopefully)
Please help me to find (and solve) corner cases, ruling issues and feel free to expand on my idea. =)
"Official Banlist" decision and explanation
See the decklist's main for, my personal try, on an ban list.
Sunder, Upheaval
Are really unfun to play against, often prolong the game, or set the caster of "bouncing everything" (or just the landbase) far, far up ahead.
Balance
Set players back and unfun to play against.
Recross the Paths
Setting up the draw order of the ENTIRE deck seems too strong, and, more importantly takes up to much time.
Demonic Consultation, Destroy the Evidence, Balustrade Spy, Consuming Aberration
Win the game on the spot, or more precisely, making everyone else losing the game out of nowhere is really unfun, just like every "normal" "win on the spot" cards.
Back to Basics
Disrupting everyone's manabase doesn't seem funny and prolonging the game.
More information about other casual variants of MTG in this link of relatively "old formats"
I know that this post is messy... :D
