Deadly Skull Storm

Split Second, Try Again & Convoke
1-8= Each player sacrifices a random creature & for
each they cannot they lose 4 life or discard a card.
9-16= All opponents sacrifice 2 random creatures &
for each they can't they lose 4 life or discard a card.
17-20= All opponents sacrifice 3 random creatures &
for each they can't they lose 4 life or discard a card.
Retrace (You may cast this from your graveyard by discarding a land card & paying its other costs)