Wall of Darkness

Defender, Gloom, Vulnerable to white (Wall of Darkness can't attack. When multiple creatures with
Gloom attack or block together, none of them die unless
they collectively take enough damage to kill all of them,
in which case all of them die. When Wall of Darkness
is targeted by a white spell or effect or dealt damage by
a white creature, it dies.)
Wall of Darkness's base power is equal to the
number of Wizards you control, and its base toughness is equal to the number of Shades you control.