Eldritch Evolution — ruling 1

Sacrificing a creature is part of Eldritch Evolution's cost. You can't sacrifice more creatures to search for more creature cards, and you can't cast Eldritch Evolution at all if you control no creatures.

Eldritch Evolution — ruling 2

Once you begin to cast Eldritch Evolution, no player may take actions until you're done. Notably, opponents can't try to remove the creature you wish to sacrifice.

Eldritch Evolution — ruling 3

A creature's mana value is determined solely by the mana symbols printed in its upper right corner (unless that creature is the back face of a double-faced card, a melded card, or is copying something else; see below). If the mana cost includes {X}, X is considered to be 0. If it's a single-faced card with no mana symbols in its upper right corner (because it's an animated land, for example), its mana value is 0. Ignore any alternative costs or additional costs (such as kicker) paid when the creature was cast.

Eldritch Evolution — ruling 4

A token that isn't a copy of another permanent has a mana value of 0. A token that is a copy or a creature that has become a copy of another permanent has the mana value of what it's copying.

Eldritch Evolution — ruling 5

The mana value of a permanent that's a double-faced card with its back face up is the mana value of its front face. The mana value of a melded permanent is the sum of the mana values of its front faces. A creature that's a copy of either has a mana value of 0.

Eldritch Evolution — ruling 6

If a card in a library has {X} in its mana cost, X is considered to be 0. If you find such a card this way, you won't have an opportunity to spend mana on {X}.

Eldritch Evolution : règles, fonctionnement et interactions (MTG)

Eldritch Evolution is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

As an additional cost to cast this spell, sacrifice a creature. Search your library for a creature card with mana value X or less, where X is 2 plus the sacrificed creature's mana value. Put that card onto the battlefield, then shuffle. Exile Eldritch Evolution.

How it works : Eldritch Evolution

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2016· Wizards of the Coast
Sacrificing a creature is part of Eldritch Evolution's cost. You can't sacrifice more creatures to search for more creature cards, and you can't cast Eldritch Evolution at all if you control no creatures.
No other card is named in this ruling.
#2July 13, 2016· Wizards of the Coast
Once you begin to cast Eldritch Evolution, no player may take actions until you're done. Notably, opponents can't try to remove the creature you wish to sacrifice.
No other card is named in this ruling.
#3July 13, 2016· Wizards of the Coast
A creature's mana value is determined solely by the mana symbols printed in its upper right corner (unless that creature is the back face of a double-faced card, a melded card, or is copying something else; see below). If the mana cost includes , X is considered to be 0. If it's a single-faced card with no mana symbols in its upper right corner (because it's an animated land, for example), its mana value is 0. Ignore any alternative costs or additional costs (such as kicker) paid when the creature was cast.
No other card is named in this ruling.
#4July 13, 2016· Wizards of the Coast
A token that isn't a copy of another permanent has a mana value of 0. A token that is a copy or a creature that has become a copy of another permanent has the mana value of what it's copying.
No other card is named in this ruling.
#5July 13, 2016· Wizards of the Coast
The mana value of a permanent that's a double-faced card with its back face up is the mana value of its front face. The mana value of a melded permanent is the sum of the mana values of its front faces. A creature that's a copy of either has a mana value of 0.
No other card is named in this ruling.
#6July 13, 2016· Wizards of the Coast
If a card in a library has in its mana cost, X is considered to be 0. If you find such a card this way, you won't have an opportunity to spend mana on .
No other card is named in this ruling.