Polymorph

Polymorph is a slang term used by Magic R&D to describe the following effect: "{Remove} target creature. Its controller reveals cards from the top of their library until they reveal a creature card. That player puts that card onto the battlefield." This effect is named after the card Polymorph from Mirage.

Description
The effect is currently primary in red and secondary in blue. For a long time, this ability was a blue thing. When R&D was looking for more places to expand red, they decided to slice up the polymorph pie. Blue gets transformations where the outcome is known and red gets them where it is not. The idea being that blue only wants to transform something when they know what they're going to get, whereas red is willing to take a risk. Red will also do large chaotic effects where many things change all at once.

Another related effect that is in between this and Transformation is when the target is replaced with a token. This effect is primary in blue, secondary in white, twice in red, and has appeared four times in green, even though the original card (Beast Within) has been an oft-cited break. Another effect that is one step removed from this, blending it with imprisoning, is when a permanent exiles a target, and the token is created for the target's owner when the imprisoning permanent is removed. This has appeared on two cards (Baffling End, Skyclave Apparition).

Creatures

 * Blessed Reincarnation - opponent's creatures
 * Divergent Transformations
 * Fireflux Squad
 * Indomitable Creativity - destroy
 * Jalira, Master Polymorphist</c> - sacrificed, only reveals nonlegendaries
 * Lukka, Coppercoat Outcast</c> - guarantees higher cost
 * Mass Polymorph</c>
 * Polymorph</c> - destroys
 * Proteus Staff</c> - puts on bottom
 * Shifting Shadow</c> - destroy, recurring Aura effect
 * Synthetic Destiny</c> - time-delay
 * Transmogrify</c>

Artifacts

 * Indomitable Creativity</c> - destroy
 * Shape Anew</c> - sacrificed

Permanents

 * Dreamshaper Shaman</c> - sacrificed, nonland
 * Reality Scramble</c> - put on bottom, shared card type
 * Reweave</c> - sacrificed, shared card type

Countering on the stack

 * Spellshift</c> - instants and sorceries
 * Tibalt's Trickery</c> - spell of a different name

Creatures

 * Afterlife</c> (1/1 white Spirit with Flying)
 * <c>Amphin Mutineer</c> (non-Salamanders, 4/3 blue Salamander Warrior)
 * <c>Basalt Golem</c> (0/2 artifact Walls with Defender)
 * <c>Baffling End</c> (3/3 Dinosaur with Trample)
 * <c>Crib Swap</c> (1/1 colorless Shapeshifter with Changeling)
 * <c>Curse of the Swine</c> (2/2 green Boar)
 * <c>Descent of the Dragons</c> (4/4 red Dragon with Flying)
 * <c>Field of Souls</c> (1/1 white Spirit with Flying)
 * <c>Gallows at Willow Hill</c> (1/1 white Spirit with Flying)
 * <c>Hour of Need</c> (4/4 blue Sphinx with Flying)
 * <c>Incongruity</c> (3/3 green Frog Lizard)
 * <c>March of Souls</c> (1/1 white Spirit with Flying)
 * <c>Mercy Killing</c> (X 1/1 green and white Elf Warriors, X is target's power)
 * <c>Mogg Infestation</c> (two 1/1 red Goblins)
 * <c>Oversimplify</c> (0/0 blue and green Fractal with X +1/+1 counters, where X is the total power)
 * <c>Ovinomancer</c> (0/1 green Sheep)
 * <c>Pongify</c> (3/3 green Ape)
 * <c>Rapid Hybridization</c> (3/3 green Frog Lizard)
 * <c>Reality Shift</c> (Manifest)
 * <c>Sarkhan the Mad</c> (5/5 red Dragon with Flying)
 * <c>Transmogrifying Wand</c> (2/4 white Ox)

Creature or artifact

 * <c>Ravenform</c> (1/1 blue Bird with Flying)
 * <c>Resculpt</c> (4/4 blue and red Elemental)

Creature or planeswalker

 * <c>Angelic Ascension</c> (4/4 white Angel with Flying)

Artifacts or enchantments

 * <c>Rampage of the Clans</c> (3/3 green Centaur)

Nonland permanent

 * <c>Cavalier of Dawn</c> (3/3 artifact colorless Golem)
 * <c>Excavation Technique</c> (two Treasures)
 * <c>Reduce to Memory</c> (3/2 red and white Spirit)
 * <c>Secure the Scene</c> (1/1 white Soldier)
 * <c>Skyclave Apparition</c> (X/X blue Illusion where X is the mana value of the exiled card)

Noncreature permanent

 * <c>Sawtusk Demolisher</c> (3/3 green Beast)
 * <c>Terastodon</c> (3/3 green Elephant)

Permanent

 * <c>Beast Within</c> (3/3 green Beast)
 * <c>Generous Gift</c> (3/3 green Elephant)
 * <c>Will, Scholar of Frost</c> (4/4 blue and red Elemental)

Spells

 * <c>Dovescape</c> (X 1/1 white and blue Birds with flying, X is noncreature mana value)
 * <c>Swan Song</c> (2/2 blue Bird with flying)