Xorn, Phyrexian Fleshsmith

Whenever a Phyrexian permanent enters the battlefield under your control, you can perpetually
place a "Compleation" counter on a target creature
in an opponents graveyard.
{x}{t} Target a opponents creature permanent that
has a mana cost equal to {x} and perpetually place a "Compleation" counter on it then take control of a Phyrexian permanent on your opponents battlefield.
"Phyresis is a process, and our soldiers can serve
whatever purpose is required of them."
-Xorn, Phyrexian Fleshsmith