Evoke

Evoke is a keyword ability that allows a player to pay an alternative cost for a creature spell that possesses this ability; however, if the evoke cost is paid, the creature is sacrificed when it enters the battlefield.
==Description==
Evoke was introduced in Lorwyn and expanded upon in Morningtide as the signature mechanic of the five-color Elementals. It began in design as a mechanic that would allow an instant or sorcery to become a creature if an extra cost was paid, but was changed to its current form due to rules limitations. All creatures in Lorwyn with evoke have a "enters the battlefield" ability, followed by those in Morningtide all having "leaves the battlefield" effects. 
Evoke allows you to play the spell for its evoke cost rather than paying its mana cost, but if you do that, you have to sacrifice it when it comes into play. This enables the player to pay the cheaper cost to just get the creature's "enters the battlefield" (or "leaves the battlefield") ability. Three evokers have evoke costs equal to their mana value and one has it above; these were all from Morningtide with "leaves" triggers, where the effect is much less predictable if left on the board as a creature.
Evoke is similar, but not identical, in concept to channel. Both are associated with powerful immortal creatures (elementals and spirits, respectively), but whereas channeling a spirit merely allows a planeswalker to tap into that spirit's power without actually summoning it, evoking an elemental brings the elemental into existence for a very brief time, whereupon its power is expended in a single moment. In mechanical terms, evoke casts and has a creature exist temporarily, opening up lines that interact with creatures, whereas channel discards, making the effect difficult to counter and always at instant speed. 
In theory, the rules would allow evoke to appear on permanents other than creatures. Part of this not occurring is due to most other permanents having no inherent impact without abilities, and as of yet all Evoke creatures are virtual French vanilla creatures. As such, an artifact or enchantment evoker would need an evoke ability, an ability that works when evoked, and an ability that matters when not evoked.
===History===
Evoke was reused sparingly in Modern Horizons and Modern Horizons 2, where the latter introduced non-mana Evoke costs (specifically, exiling a colored card, resulting in pitch spells). It also appeared in Modern Horizons 3. All creatures with evoke have continued to be Elementals in race.
Mark Rosewater expects evoke to make a return, possibly also on noncreature permanents.
==Rules==
==Rulings==
*Casting a creature by paying its evoke cost will result in two enters-the-battlefield abilities: The sacrifice ability from evoke, and whatever other ability the creature has. The creature's controller chooses in what order to put them on the stack. Both abilities can be responded to as normal.
*Evoke doesn't change the timing of when you can cast the creature that has it. If you could cast that creature spell only when you could cast a sorcery, the same is true for casting it with evoke.
*If a creature spell cast with evoke changes controllers before it enters the battlefield, it will still be sacrificed when it enters the battlefield. Similarly, if a creature cast with evoke changes controllers after it enters the battlefield but before its sacrifice ability resolves, it will still be sacrificed.
*When you cast a spell by paying its evoke cost, its mana cost doesn't change. You just pay the evoke cost instead.
*Effects that cause you to pay more or less for a spell will cause you to pay that much more or less while casting it for its evoke cost, too. That's because they affect the total cost of the spell, not its mana cost.
*Whether evoke's sacrifice ability triggers when the creature enters the battlefield depends on whether the spell's controller chose to pay the evoke cost, not whether they paid it (if it was reduced or otherwise altered by another ability, for example).
*If you're casting a spell "without paying its mana cost," you can't use its evoke ability.
==Examples==
==References==