The Astral Set from Shandalar a.k.a. Magic the Gathering: Duels of The Planeswalkers
The Astral Set from the MicroProse Magic the Gathering computer game released in 1997 contained cards that could not exist outside of a computer.
Because these cards featured random effects, that would be hard to truly randomize in the real game, they exist only within the game.
Below are those twelve cards:
When Aswan Jauar comes into play, choose a random creature type form those in target opponent’s deck.
[Two Green Mana] [TAP]: Bury target creature of the chosen type.
Call from the Grave
Put a random creature from a random graveyard into play under your control. Call from the Grave deals you an amount of damage equal to that creature’s casting cost.
When Gem Bazaar comes into play, choose a random color.
[TAP]: Add to your mana pool one mana of the chosen color. Then choose a random color.
Goblin Polka Band
[Two Colorless Mana][TAP]: Pay [One Red Mana] for each target: Tap any number of random target creatures. Goblins tapped in this way do not untap during their controllers’ next untap phases.
Necropolis of Azar
Whenever a non-black creature is put into any graveyard form play, put a husk counter on Necropolis of Azar.
5, remove a husk counter from Necropolis of Azar. Put a Spawn of Azar token into play.
Treat this token as a black creature with a random power and toughness, each no less than 1 and no greater than 3, that has swampwalk. (If defending player controls any swamps this creature is unblockable.)
Randomly distribute X -0/-1 counters among a random number of random target creatures.
[Three Colorless Mana] [TAP]: Choose a random summon card from all player’s decks. For each player, flip a coin.
If the flip ends up head, put a token creature into play and treat it as though an exact copy of the chosen summon card were just played.
During each player’s upkeep that player exchanges control of random target artifact, creature or land he or she controls, for control of random target permanent of the same type that a random opponent controls.
Flying. During your upkeep, Prismatic Dragon becomes a random color permanently.
2: Prismatic Dragon becomes a random color permanently.
When Rainbow Knights comes into play it gains protection from a random color permanently
[One Colorless Mana]: First strike until end of turn.
[Two White Mana]: +0/+0, +1/+0 or +2/+0 until end of turn chosen at random.