Magic: The Gathering is the first and most popular collectible trading card game, released by Wizard of the Coast in 1993 and expanded multiple times a year, even outsourcing its lore now with Universes Beyond cards from for example Warhammer 40,000. Only official white- or black-bordered cards without acorn stamps are valid in tournament play.
100-card singleton (only basic lands can have any number), 40-life, 4-player games are most popular. This format is called Commander, or Elder Dragon Highlander (EDH) originally. Your deck then has one legendary creature as leader in the command zone, costing 2 mana more for each time it has been cast from there, and can be returned to there if it changes zone. Hand, battlefield, graveyard, exile, and library are also zones, sometimes denoted on a playmat. 21+ damage from the same commander card is lethal, no matter one's life total. There are 5 colors of mana (magic points), and your commander's determine which can be in your deck:
| Color | Theme | Known for |
|---|---|---|
| White (W) | Order | Angels |
| Blue (U) | Control | Merfolk |
| Black (B) | Greed | Demons |
| Red (R) | Freedom | Dragons |
| Green (G) | Growth | Hydras |
Opening hand is 7 cards, minus one to the bottom of your deck for each time you take a mulligan by shuffling and drawing a new opening hand. With 3+ players, the first mulligan is free and the starting player also draws at the beginning of their first turn.
You can play one land per turn. Tap (turn sideways) lands for mana to cast spells. Spells are played on a shared stack, passing priority in turn order to respond before resolving the top spell or effect from an activated ability (Preceded by a colon: :.), static ability (like flying), or triggered ability (identified by the words "when," "whenever," or "at"). Mana abilities don't use the stack.
The most counterintuitive Magic rule is Song of the Dryads turning a creature like Bello, Bard of the Brambles into a colorless Forest land and implicitly removing Bello's abilities, yet Darksteel Mutation which explicitely removes abilities not doing so before Bello's abilities do their thing.
Some old cards have had their text changed. See the Oracle text for it in the Companion app or on Gatherer. Oracle text overrules card text, and in casual, house rules overrule that.
It is polite to decide on a power bracket when picking a deck for a casual game. That adds an additional list of restricted cards (not all cards are valid in every format, see the Oracle per card), but I find it easier to take your average win turn against a goldfish:
| Bracket | Usually wins in turn |
|---|---|
| 1 (flavortown/random) | 10+ |
| 2 (preconstructed/out-of-the-box) | 8 |
| 3 (upgraded precon) | 6 |
| 4 (optimized) | 4 |
| 5 (cEDH/competitive) | 2 |
Games take about 2 minutes per turn; 4-player bracket-2 game an hour; 4-player bracket-5 game with banter in 16 minutes.
It is recommended to at least use (standard size) penny sleeves to keep your cards unmarked and test unowned cards digitally, like on Arena. Printing proxies is often allowed in casual, but like buying singles with unlimited money, not the way it was meant to be played.