Lula's Library Shredder

(You may cast a legendary sorcery only if you
control a legendary creature or planeswalker.)
Each opponent mills a card, discards a card, and
draws a card. If this spell's Flashback cost was
payed, instead each opponent mills X cards,
discards X cards, and draws X cards
Flashback {x}{u}{b}{r} (You may cast this card
from your graveyard for its flashback cost.
Then exile it.)