Highlander is a casual constructed variant of Magic which allows only one copy of each card in the deck, with the exception of basic lands.  The name Highlander is a reference to the movie of the same name, whose tag line was "There can be only one". 
- Any card from Alpha up through the latest Magic set can be used (except for banned cards). Cards from the Portal sets, International Collector Editions, and Championship decks can be used provided you put all your cards in opaque sleeves and the International Collector Edition card edges are rounded.
- Special mulligan rule: The first time a player takes a mulligan, he or she draws a new hand of as many cards as he or she had before. Subsequent hands decrease by one card as normal.
As a casual format, individual playgroups often have their own house rules regarding almost any aspect of the game to suit their own style and to make the game more fun. This often includes a more extensive banned list, or banning certain combinations (e.g decks can include a Thopter Assembly or a Sword of the Meek, but not both) or modifying how interactions work (e.g. infinite loops only recur a set number of times to prevent infinite damage or mana loops that would otherwise win the game immediately). In these cases the objective is to lengthen the game and prevent good draws from being able to win or knock a player out of the game too soon. Given how big the card pool is, there are many plausible, if unlikely given the format, ways to deal infinite damage or otherwise win within a few turns and this is generally considered to not be in the spirit of the game, and can be enforced with house rules if the group feels they need to.
Versions of the game can be found that include practically any imaginable permutation of game rules that emphasize different aspects of the game. Some groups prefer to play using older sets of rules (combat damage still going on the stack being particularly popular) while others use a random turn orders or may even apply 'end of turn' effects until the end of the turn sequence (i.e. until the player before you completes their turn) to change the dynamic of the game. Other groups emphasize the creative aspect of the game by creating a set of homebrew cards that can be added to decks. Finally, some groups focus on the social aspect of the game, adding rules for alliances or a dedicated politics phase to the turn, when players can scheme. On the less serious end of the spectrum, there is a Commander drinking game that can be played, where every time you cast your general you have to finish a drink.
- A deck may not contain two cards with the same english name except basic land cards.
- A deck must contain at least 100 cards.
- Some cards are entirely banned in tournament formats. Since these are non-DCI-tournaments, they have individual ban lists. 
- No sideboards are used.