Extronum, Robot Tyrant.

This spell cannot be countered.
Defender, Hexproof
{4}: Cast 2 cards from any graveyard without
paying the mana cost.
{t}{5}: Destroy all permanents under each
opponents control.
{t}{5}: All opponents exile {x} cards from their
library, where {x} is the total amount of cards in
all graveyards.