Shriek of Blood Despair

Shriek of Bloody Despair can't be countered.
Choose one —
• Each opponent sacrifices eight creatures.
• Add {8}{b}{b}{b}{b}{b}{b}{b}{b} to your mana pool.
• Cast up to two target cards from graveyards
without paying their mana costs.
Flashback {1}{b}{b}{r} (You may cast this card from
your graveyard for its flashback cost. Then exile it.)