[steveklabnik]

Originally, the 4 copy maximum didn't exist. However, there were two early decks that broke the game:

  20x Black Lotus 
  20x Channel 
  20x Fireball 

Gatherer links: http://gatherer.wizards.com/Pages/Card/Details.aspx?multiver... http://gatherer.wizards.com/Pages/Card/Details.aspx?multiver... http://gatherer.wizards.com/Pages/Card/Details.aspx?multiver...

As long as you get 2x Lotus, 1x other two in your opening 7 cards, first turn kill. Play two lotus, sacrifice one for green, one for red. Play channel with green. Give up 19 life. Do 22 damage with Fireball.

Black Lotus is worth five figures these days, so building that deck would be very expensive. Replacing them with Mountains and Forests gives you a deck for less than ten dollars that can routinely kill on the fourthish turn every time, though.

The second one is even sillier: (see edits and citations below, I slightly mis-remembered this one, but the concept is the same)

  60x Shahrazad

http://gatherer.wizards.com/Pages/Card/Details.aspx?multiver...

This was Richard Garfield's favorite card. But due to the way the rules work, a subgame within a subgame within a subgame within.... means that you win, due to the way that rounding works.

[herbig]

Even better is:

  31 Ancestral Recall
  25 Black Lotus
  3 Timetwister
  1 Braingeyser

You don't need 2x of any one thing to get started, you only need 1 Lotus and 1 Timetwister or Ancestral Recall.

If anything gets countered, you are very, very likely to be able to keep going and win the same turn.

Timetwister lets you recycle, so you can generate infinite mana.

Braingeyser kills the opponent, and doubles as card draw itself, in the unlikely event that you stall out.

You also don't lose to a turn 1 Lightning Bolt, like you do with Channel.

A mulligan to two still has a fairly high likelihood of winning on the first turn.

[steveklabnik]

Ah nice!

[javajosh]

Shahrazad, aka MTG virtualization. Too bad there aren't other ways to encode bits. Also, if you lose half your life and you're at 1, what happens?

[steveklabnik]

  > Too bad there aren't other ways to encode bits.

Well, I mean, if you look at the article, it encodes a turing machine, so... oh man what about playing Shahrazad inside of the turing game...

  > Also, if you lose half your life and you're at 1, what happens?

So there's an entire section of the rules that had to be added, just for Shahrazad. http://media.wizards.com/images/magic/tcg/resources/rules/Ma... is the link, Section 715, subgames. Now that I'm re-reading, I _think_ that you actually win by decking, not by life: you just play with a larger than usual deck, and

  715.3. Because each player draws seven cards when a game begins,
  any player with fewer than seven cards in his or her deck will
  lose the subgame when state-based actions are checked during the 
  upkeep step of the first turn, regardless of any mulligans that 
  player takes. (See rule 704, “State-Based Actions.”)

Here's the citation for it being Richard's favorite card, and a commentor leaves an explanation: https://www.reddit.com/r/IAmA/comments/20f1dn/we_are_richard...

Mox Pearl is simpler and faster than Plains!

[AlexTFish]

The Shahrazad deck also presumably needs either Plains or Black Lotus.

[steveklabnik]

Ahh yes, good call. I will leave my post the way it is to leave your reply coherent, my mental model was "Only Shahrazad", which is true, but you still need to pay for it...

EDIT: Looks like Mox Pearl is the right way to go.