Bo'kahn, the Blood-Cursed

Cull the Herd —As an additional cost to cast this
spell, you may sacrifice any number of creatures.
This spell costs {b} less to cast for each creature
sacrificed this way.
Whenever Bo'kahn, the Blood-Cursed attacks,
for each creature you sacrificed this turn, choose
an ability from among first strike, deathtouch,
lifelink, and menace. Bo'kahn gains the chosen
abilities until end of turn.