Eldos, Piper of the Damned

Whenever a creature an opponent controls dies,
you may exile Eldos, Piper of the Damned. if you
do, return that creature to the battlefield under
your control with a song counter on it.
Whenever a creature you control with a song
counter on it leaves the battlefield, you may put
Eldos, Piper of the Damned into play under your control from exile.