Sylvia, Woodland Protector

Double Strike, Vigilance
Other elves you control get +0/+2 and have vigilance
At the beginning of each end step, if 3 or more
elves you controlled died that turn, you may pay {b}{b/g}{g}. If you do, exile Sylvia, then return her to
the battlefield transformed under her owners
control.
(transforms into Morwen, Fallen Leader)