The River Styx

This card comes into play tapped.
Tap ({t}) to add either {w}, {u}, or {b}.
When River Styx comes into play, separate the battlefield into two sides. Put all creatures in
graveyards under their owner's control on one
side. The other side is the creatures in play.
Creatures on the dead side have Shroud.
When combat begins, players may attack from
either side of the river. When a creature on the
dead side dies or leaves play, exile it.