Zant, Usurper King

If Zant, Usurper King, is your commander,
you can have both {w} and {b} cards in
your library regardless of Zant, Usuper
King's mana type. Zant, Usurper King
can be in a {b} commander library
even if that commander does not have {w}
in their mana type.
If Zant, Usurper King defeats a {w}
creature with 4/4 or more,
create a 4/4 Shadow Beast (TP).