Akrad, Corrupted Prince

Horsemanship
Whenever Akrad, Corrupted Prince attacks, defending player bids
any amount of life. Then you may top the high
bid. The bidding ends if the high bid stands.
The high bidder loses life equal to the
high bid, and then creates X 1/1 black Skeleton
Knight creature token with horsemanship
and "Sacrifice this creature at the beginning of
your end step".