List of unreleased mechanics

There are some mechanics that have been designed by R&D but have been never released for several reasons as rules concerns. Some of them have been publicly explained over the years.

Unreleased colors

• Purple — For Planar Chaos.

Unreleased counters

• Volatile counters — By Mark Gottlieb, for Aether Revolt. When a card with a volatile counter dies, it deals 2 damage to target opponent.

Unreleased keyword actions

• Double-tap — For Time Spiral. Cards that could tap, then tap again. Led to exert.
• Hedronize — For Battle for Zendikar. Roll a d8 and trigger a different effect depending on the value rolled.

Unreleased keyword abilities

• Advocate — for Commander Legends. A triggered mechanic (like landfall or constellation) that triggers whenever your commander enters the battlefield or attacks.
• Anchor — For Time Spiral. ig creatures for cheap that required a mana payment for upkeep.
• Bribe — for Conspiracy: Take the Crown and Commander Legends. The spell gives you an effect. Then, each of your opponents may choose to draw a card. For each one that did, you get the effect again.
• Call — for Ixalan. A Dinosaur with call was usually a bigger Dinosaur, but one with a very cheap mana cost. You couldn't attack or block until you paid a one-time activation cost.
• Camouflage (As long as this is untapped, it can't be the target of spells or abilities your opponents control) for Ikoria: Lair of Behemoths. This is similar to Paradise Druid.
• Clan — for Kaldheim. A modified version of Leader, adapted for use as a tribal mechanic. When you played a clan card, you chose a creature type, and the card affected that creature type. Then when you played a second clan card, you could rechoose your creature type, but both effects would affect the one chosen tribe.
• Conjure [creature type] – [cost] — for Strixhaven: School of Mages (If you cast this spell for [cost], when it enters the battlefield create an [appropriately sized, colored, and creature-typed] creature token.)
• Cooperation (Whenever this creature deals combat damage to a player, put a +1/+1 counter on another target creature.) for Throne of Eldraine. A variant of the Slith mechanic.
• "Creaturefall" — for Selesnya in Guilds of Ravnica. Effects that trigger whenever a creature you control enters the battlefield.
• "Deathfall" — for Jund in Shards of Alara. Effects that trigger every time a creature dies.
• Debt — for Orzhov in Ravnica Allegiance. Spells give debt counters to opponents. At the beginning of their end step, they can get rid of any number of debt counters by paying per debt counter. Then, as long as they have any debt counters remaining, they lose 1 life (not per debt counter just 1 life total regardless of how many debt counters they have).
• Discipline N (Whenever this card becomes blocked, put N +1/+1 counters on this card.) for Throne of Eldraine.
• Disguise — for Dimir in Guilds of Ravnica. A ninjutsu variant where the creature with disguise is swapping with the attacking creature.
• Enhanced — for Kaldheim. Enhanced meant that a creature was either enchanted or equipped. The ability went on creatures and gave them an extra ability if they were enhanced.
• Enlist — for Ixalan. Pay extra mana to create a creature token.
• Familiar – [Effect] — for Strixhaven: School of Mages (. . . if you control a creature token).
• Finale — For Rakdos in Ravnica Allegiance. Creature gains +N/+0 and some abilities, in exchange for being sacrificed at the end of turn.
• Forbidden — By Mark Rosewater, for Avacyn Restored. Card starts the game in exile.
• Glorify — For Amonkhet. If this creature dies when attacking, it grants a bonus to another creature.
• Gunk — By Richard Garfield. Blank cards that didn't do anything but could be transferred to the opponent's deck. It later appeared on a test card in the Mystery Booster set.
• Hieroglyphics — By Mark Rosewater, for Amonkhet. Pay to exile the card from the graveyard and draw a card.
• Jewel — For Guilds of Ravnica. It went on any instant or sorcery. After the card resolved, it got exiled. Then, whenever you cast another instant or sorcery, you could play the first card for free from exile. The idea behind it was that we built smaller effects that comboed together to do cool things.
• Joust (When this creature is blocked, it gets +0/+N until end of turn. If not blocked, it gets +N/+0 instead.) for Throne of Eldraine.
• Leader — for "Salad", an unmade set intended to follow on from Dominaria. Whenever you played a leader card, you chose a leader from among your creatures, and that card granted an ability to your leader. If you played a second leader card, you had the option of changing who your leader was, but both cards would grant abilities to a single leader.
• Mechanic I — For Kaladesh. The only unexplained mechanic of the five that the Kaladesh design team ended up making and liking. It got discarded for excess of mechanics.
• Mummify — For Amonkhet. As embalm or eternalize, but makes the creature a 2/2 Zombie with wither.
• Nostalgia — By Mark Rosewater, for Time Spiral. It allowed you to put Vintage-legal cards into your deck that you might not normally be able to play.
• Paincast — For Rakdos in Return to Ravnica. Spells 1 mana cheaper for each point of damage you had dealt to an opponent this turn.
• Plot — For Amonkhet. A suspend variant representing you planning ahead.
• Plunder — For the Vampires and Pirates of Ixalan. Based on bloodthirst. When you cast these cards, if you had dealt combat damage to an opponent, the card received some kind of bonus.
• Precedence — For Azorius in Ravnica Allegiance. When this enters the battlefield, copy the ETB ability of any other creature you control.
• Reckless — For Gruul in Gatecrash. An ability that sacrificed the creature at the end of the turn when triggered.
• Relentless — For Time Spiral and inspired by Relentless Assault. Allowed creatures to attack twice each turn.
• Resistance (This creature isn't a legal target of a spell or ability an opponent controls unless they pay as that spell or ability resolves) for Ikoria: Lair of Behemoths
• Reverse Engineer — For Kaladesh but pushed for Aether Revolt. It allowed you to copy an artifact and then that copy got sacrificed at end of turn, in the same way Heat Shimmer from Lorwyn does for creatures.
• Roar — By Mark Gottlieb, for the Dinosaurs of Ixalan. "You may pay [cost] and exile this card from your hand. If you do, you can still cast it this game. When CARDNAME roars .... [effect]". Led to Adventure.
• Scrolls — for Strixhaven: School of Mages. The idea of scrolls was that they were artifact tokens that could hold an instant or sorcery in them. You then sacrificed them to cast the spell it was holding. Some cards let you make scrolls out of available instants or sorceries. Other cards made scrolls with spells (usually famous ones from Magic's past) already inside them.
• Showoff — By Mark Rosewater, for Lorwyn. It allowed you to choose to reveal a card. If the card was revealed (from your hand or your library), then it could be played for its showoff cost, which was often cheaper than its normal mana cost.
• Skirmish — for War of the Spark. "Create a Skirmish if one hasn't been created yet." The Skirmish token has a tiny "game board" on it showing a field of combat. When you perform one of the stated conditions, you advance on the field toward the opponent's side. If you have advanced enough, you win the skirmish. There is a payout for winning, a generated effect.
• "Sneaky" (This creature can't be blocked by creatures with power 3 or greater) for Ikoria: Lair of Behemoths.
• Spellback — for the Izzet League in Guilds of Ravnica. Somehow allowed players to "mix and match various instants and sorceries".
• Stopwatch — mechanic forces you to do certain actions in a set amount of time. Considered for Unstable.
• Stygian — for Theros Beyond Death. When you play a card with the stygian mechanic, it brings onto the battlefield a special card from outside the game that represents the river of the dead. Creatures on the living side could only block creatures also on the living side while creatures on the dead side could only block creatures on the dead side.
• Titan — for Zendikar Rising. A kicker variant where the mana cost was always generic and always seven or more mana. It tended to mega-juice the spell. The flavor was that you were tapping into some residual Eldrazi energy that was seeped deep in the land.
• Torment — Each opponent loses 3 life unless that player sacrifices a nonland permanent or discards a card. Reduced to an unkeyworded vertical cycle in Hour of Devastation.
• Turmoil — For Gruul, then Rakdos in Ravnica Allegiance. Effect that triggered at the end of your turn if an opponent had lost life during that turn.
• Unique — By Mark Rosewater, such mechanic is intended to narrow the Legendary rule effect which would be applied only to legendary permanents having the Unique ability.
• Unnamed — By Mark Rosewater, for Tempest. It allowed you to choose to start with the card in your opening hand. If you chose to do so, you had to begin with one card fewer.
• Unnamed — For Amonkhet. It made use of -1/-1 counters to represent the ruthlessness of Bolas.
• Valiance (Whenever this creature deals combat damage to a player, put a +1/+1 counter on it.) for Throne of Eldraine. This is the Slith mechanic.
• Ward (Once each turn, you may draw a card while this creature's the target of an opponent's spell or ability) for Ikoria: Lair of Behemoths

Unreleased lands

• Barry's Land — By Mark Rosewater, for Invasion. Later by Bill Rose, for Conflux. Printed as a test card in the Mystery Booster set.
• Cave/City — See Purple.

Unreleased subtypes

• Quest (other mechanic than the released Quest enchantment) — For Zendikar and Throne of Eldraine. Enchantments that gave you three tasks. You marked them with counters as you finished each one. Once all of them were completed, you could sacrifice the card for a big effect. Some got you the legendary artifacts for each court.
• Inventions — for Kaladesh. Cards that let you fetch artifact cards from outside the game. Released in Eldritch Moon as meld.
• Mechanic E — By Mark Rosewater. Mechanic E, "energy", was originally designed for Mirrodin and finally printed in Kaladesh as energy counters.
• Pwnage — By Ken Nagle, for New Phyrexia. It allowed you to shuffle cards from your opponent's library into your own. It was killed by the rules, but released as Praetor's Grasp.
• Q-mechanic — By Mark Gottlieb, for Shadowmoor. It became the untap mechanic ().
• Triple strike — By Mark Rosewater, for Future Sight. Released in Unstable.