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

• 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.
• 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).
• "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.
• Disguise — for Dimir in Guilds of Ravnica. A ninjutsu variant where the creature with disguise is swapping with the attacking creature.
• Enlist — for Ixalan. Pay extra mana to create 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• Spellback — for the Izzet League in Guilds of Ravnica. Allows 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.
• Torment — Each opponent loses 3 life unless that player sacrifices a nonland permanent or discards a card. Reduced to a 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, to replace Legendary.
• 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 — By Mark Rosewater, for Time Spiral. It allowed you to put cards into your deck that you might not normally be able to play. The idea was the card say that if it was in your deck, then you were allowed to have up to four copies of a card from the past in your deck —even if that card wasn't normally legal in Standard. Understanding that those cards might not be broken cards, Mark Rosewater found six subsets of past cards, one for each color and one artifact, that could work —blue's member of this cycle was a creature that had the creature type Wizard.
• Unnamed — For Amonkhet. It made use of -1/-1 counters to represent the ruthlessness of Bolas.

Unreleased lands

• Barry's Land — By Mark Rosewater, for Invasion. Later by Bill Rose, for Conflux.
• Cave/City — See Purple.

Unreleased supertypes

• Über-classes — By Mark Rosewater, for Morningtide. Cards that affected "fighters" affected Soldiers and Warriors (and possibly Knights). "Mages" were Shaman and Wizards (and possibly Druids). "Scoundrel" meant Assassins and Rogues.

Revealed mechanics

These formerly unreleased mechanics were eventually used in new sets.

• Assemble — Printed on a single card in Future Sight, but without any associated mechanical definition. Released in Unstable.
• Last strike — By Mark Rosewater, for Future Sight. Released in Unstable.
• Link — By Ken Nagle, for New Phyrexia. Supposedly the same [Redacted] mechanic that Aaron Forsythe hinted. 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.

References

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