Rules for Multiplayer Constructed Tournaments Or Gameplay
Deck Size Limits:
Constructed decks must contain a minimum of sixty cards. There is no maximum deck size; however, players must be able to sufficiently randomize their deck within the time allotted.
Multiplayer Constructed tournaments use Unified Deck Construction rules:
With the exception of basic land cards, a team’s combined decks may not contain more than four of any individual card, counted by its English card title. (For example, if one player is using four copies of Naturalize in a Multiplayer Constructed event, no other player on that team may have a Naturalize in his or her deck.) If a card is restricted in a particular format, no more than one of that card may be used by the team. No players may use cards that are banned in a particular format.
In addition to cards banned in particular formats, the following card is banned in ALL Multiplayer Constructed tournaments (Vintage, Legacy, Extended, and Block):
Erayo
Soratami
Ascendant
Sideboard Use:
Sideboards are not allowed in Constructed Multiplayer tournaments. But playing for fun is fine. =P
Note: Let me know if there are any errors or if it's not updated to it's newest status.
Links to MTG related sites for reference:
Online buying of Magic The Gathering cards:
http://www.mtgfanatic.com/
Wizards of The Coast Official Website:
http://www.wizards.com/
For MTG section on the Wizards site go here:
http://www.wizards.com/magic/
Magic The gathering reference websites:
http://www.cardkingdom.com/
http://www.moxdiamond.com/Magic-The-Gathering-Search.html