Rennala, Lunar Queen

{x}, sacrifice an artifact: Target creature with
mana value X becomes the color and creature
type of your choice and loses all counters. you
may change that creature's power and toughness,
the sum of both must match the sum of its
original power and toughness. A creature's
toughness cannot be reduced to 0 in this way.
Any player may activate this ability.
"Hush, little culver. I'll soon birth thee anew,
a sweeting fresh and pure..."