Xix, Embodiment of doom

Shadow, Deathtouch, Indestructible
As an additional cost to cast Xix, Embodiment of doom, Pay 5 life.
Whenever a creature dies, add {b}
You don't lose {b} due to phase change.
{t},{b}{b}{b}{b}{b}, Pay 20 life, Sacrifice 5 creatures, Sacrifice a land, Exile Xix: You win.