The horse of Death

Afterlife 5
When horse of death enters the battlefield, pay {x}. Then search your library for X number of black planeswalkers and put them on the battlefield.
{4}: Search your library for a black planeswalker and put it in your hand
{6}: Search your library for a black planeswalker and put it on the battlefield
{x}{x}, Search your library for X number of black planeswalkers and put them in your hand