Type 4! (Rif-raf calls it 'limited affinity', I thought I'd share some more info about this fantastic format :D)
You make one deck which is shared by all players. It includes X cards, whatever cards you can find that would work great in them. You'll know what I mean later.
Each player draws 7 cards from the pile. Now, this is the catch: There is no mana. You can play cards with any converted mana cost, colour, or spell type. BUT, you can only play one card each turn!
So, the kind of deck that you'd want to build would have been by the following rules:
No lands whatsoever, you don't need it anyway. There's special lands, yes, but other cards are way better.
Get the most overpowered creatures in it. Lorthos, the Tidemaker, anyone?
Powerful spells. T4 is a game in which everyone has his instants ready to respond to anything that is played in an opponent's turn. You have one spell each turn, why not use it?
A personal favorite
- Abilities. It's a MUST. Cards with morph, "Tap: Do insane damage to whatever target", stuff like that. The heavier the better.
Try it out! It's great fun, especially with like 6 or more players. And it's not like you'd play those cards in standard normally...
- Have enough cards. Try to use cards from a lot of editions. Whenever a new one is released, search for cards I've mentioned above. Decks can have any number of cards, the more you have, the less frequent some become.