Eldritch Evolution

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.

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.