Meta-Magic Design, or, "'Restart The Game' Is A Complete Sentence"
@patricia-taxxon's new video essay on Celeste modding has a great bit about mods as fanfiction of a game's mechanics, and it's interesting to use that lens on thirty years of variably-canonical Magic: The Gathering design. (As with her video, this will necessarily have a lot of game jargon but the broad strokes should hopefully be clear.)
Level One: Standard-legal expansions, the most accessible and promoted sets, which generally follow an ongoing storyline and introduce/reuse named mechanics. (Standard is one of the game's most-played competitive formats, made up of the last ~two years of main sets.) They have their set of characters who may show up in new incarnations, turned evil, turned good, etc. but are mostly constrained by who's currently alive and relevant.
In addition to the named mechanics, there are plenty of established design tropes at both the card and set levels: Cancel With Upside. a 2/1 for B that can't block, or ETBs tapped, and has some way to recur itself. Common tapped dual lands with marginal upside. An instant for 1B that kills most creatures in the game but with enough relevant exceptions for interesting counterplay. A cycle of two-color uncommons that clearly signpost draft archetypes. At the set level, R&D has frameworks for the quantity and efficiency of removal, the range of creature sizes, the mix of payoffs and enablers and counterplay for the set's mechanics.
These frameworks can be nudged depending on the feel the set's going for: Innistrad's creatures were a bit squishier to better set up Morbid, multicolor-themed sets will (usually) have better mana-fixing, etc. Sometimes R&D just fucks up, like making a set way too aggressive or way too grindy, but usually these deviations have some cleverness behind them.
Level Two: Supplemental sets, like Modern Horizons and Commander products. They have greater leeway to make weirder, wordier cards, bringing back and remixing old mechanics, and featuring long-dead or obscure characters, all in service of targeting a more enfranchised audience. Standard-legal sets will have their fair share of cards that look alright but truly shine if you're aware of the game's high-level strategy and rules implications, but these sets can have cards that only make sense if you do, or push those rules to the limit. Standard-legal sets have flirted with this zone, like the polarizing meta-jokes of Time Spiral block - hell, Modern Horizons was internally pitched as Time Spiral 2. This is the zone of cards with no mana cost - not zero, but nonexistent - and design puns like combining the Splice mechanic with the established motif of Splicers-who-make-golems. These sets will also bring back both underused and notoriously-broken mechanics and themes, aiming to readjust the power level up or down as needed. These sets have admittedly produced some spectacularly broken cards, but it is pretty neat to see a banned card that literally says "You can't spend mana to cast this spell."
---THE THRESHOLD OF TOURNAMENT LEGALITY---
Level Three: Non-tournament-legal cards printed by Wizards of the Coast. Most of these are in the Un- sets, with a wacky tone poking fun at the game's self-serious lore, and designs ranging from "intuitive to say plainly, but do not work in the game's rules grammar" to "Slaying Mantis enters the battlefield by being thrown from a distance of at least three feet." There are also the more deadpan Playtest Cards, which are closer to the casual way card text is written out before editors hammer it into the game's rules language. They reference past design experiments and ideas from the Great Designer Search competitions alongside things that would make the rules manager stab you if you proposed them seriously. (Though, much as Un- sets have often been a testing ground for Level Two designs, one playtest card has already been reprinted under a new name in a standard-legal set.) These are free to be fully disregard the fourth wall and play in bizarre territory, and all levels of the game are richer for it.
Level Four: Fanmade cards that Wizards employees legally cannot look at or acknowledge, except for very specific circumstances like Great Designer Searches or the You Make The Card events. These are free to seriously imitate any of the above levels, reference media Wizards never could or would, be straight-up jokes rather than game pieces, or just riff on the Custommagic subreddit's abiding love of Colossal Dreadmaw. A few brave souls make whole custom sets meant to be drafted, which demands a rigorous level of design and playtesting but also frees them from the cards having to be playable (or non-broken) in broader formats. Maybe the perfect payoff card the set needs would break Modern in half; that's not their problem. Although this level is almost completely walled off from the conversation among the first three, plenty of Great Designer Search finalists (and winners!) came up in this realm and bring its sensibilities with them.
On one hand there are the game's textual rules, named mechanics, design tropes, and established tone; on the other, the set of brain-melting rules interactions, the mechanics that flopped, play patterns considered brutally unfun, and Noggin Whack. The game would calcify if R&D stayed safely within the first realm, and although they have been rightfully criticized for some of their ventures outside it, there's a lot to learn from the wilderness.