Star

Star (also known as Pentagram or Five-Point) is a constructed Magic: The Gathering format that is played by five players, each representing one of the five colors of Magic (white, blue, black, red and green). Decks may not include any cards of a different color or a land that produces a different color of mana.

Description
Players sit in the circle specified on the back of every Magic card. Gameplay goes clockwise around the table. Determine the starting player randomly, as usual. A player wins when the players behind the two enemy colors have been eliminated, regardless of who eliminated them, although defeated players cannot win. Players cannot attack allied colors by default.

Star can be played with any format - Casual, Standard, Commander, Legacy, Modern, etc. Star games tend to end more quickly than free-for-all games due to only needing to defeat two players rather than the entire board.

Allied-Color Star
While one-color Star is the most common form, it's possible to construct a game of Star that uses two-color decks with allied color pairs: i.e., one deck for each of, , , , and. Players are seated similarly to how they are in one-color Star but placed according to the gaps between adjacent colors rather than at each color dot. As with one-color Star, decks may not contain any cards which reference colors, not in their deck, or lands that produce a different color of mana. Lands or other effects which produce mana of any color are treated as producing either of the deck's colors.

Players win the game when both players using their deck's common enemy color are eliminated: for instance, the player wins when both the  and  players have been eliminated, as green is the common enemy of blue and black. As with one-color Star, two players can both win the game.

Double Star
It's possible to combine regular and allied-color Star deck sets to play a ten-player game of Star. The single-color decks are seated as in the pentagon, with each dual-color deck seated between its constituent colors; i.e., the player sits between the  player and the  player. A player is allied with the two players closest to them on either side and enemies with the five players opposite them. A player wins when their five enemies have been defeated; for example, is allied with, , , and , and wins the game when , , , , and  have been eliminated.

No color restrictions
Star can be played without deck construction color restrictions and with any number of players. This can be helpful for playgroups that like the shorter games Star can produce but don't necessarily have enough monocolor decks handy. A player wins when the players who begin the game seated directly across from them are all eliminated.

If playing with a number of players other than 5, use common sense - in a six or seven player game, each player wishes to defeat the three enemies across from them; in an eight or nine player game, the victory condition is eliminating four enemies; and so on.

Victory conditions
Star can be played such that even defeated players can win the game once their two opponents are defeated. This guarantees the game will end once 3 players are defeated. This variant does mean that it is possible to be in a "dead man walking" situation if a deck doesn't have the capability to defeat two decks simultaneously - for example, if White and Black are eliminated, then the Blue player now needs to simultaneously defeat Green and Red, since defeating just one of them will merely result in an already defeated player winning. (Even defeating both simultaneously will only mean a shared three-way victory if you play with this rule.)

Attacking allies
Star can also be played where attacking an ally is allowed (in the sense of creatures going to the attack step - targeting an ally or an ally's spells is always legal). This is only situationally useful even if allowed, but you never know.

Another potential issue of variance is whether everyone at the table is an opponent, or if allies do not count as opponents for the sake of cards that specify opposing players. This is relevant for cards such as or  - do they deal damage only to the opposing colors, or to everyone else? Note that if playing where everyone counts as an opponent, there are some potentially odd plays this opens up, especially if two allied colors decide to work together for a simultaneous victory - cards such as (an ally might offer a 5/0 split if they count as an opponent) or  (both allies draw their deck), so use common sense.

Color hosers
The group should decide beforehand if color hosers are acceptable, or if they should be limited or banned outright. Since hosers can be exceptionally strong in this format, best make this clear in advance. "Some Star groups banned color hosers outright, others established a "two hoser" rule or similar to keep things fair but occasionally spicy, and I'm quite sure that somewhere, some mad band of misanthropes allowed any and all hosers, and spent a great deal of game time swearing at each other in the wake of an endless parade of,, , etc."

- Kelly Digges

Cards that hose mono-colored decks such as might also be worth mutually agreeing beforehand on if they are expected in-game, since everyone will be playing monocolor.