Ragnar, the Primordial Being

Intimidate, menace
When Ragnar enters the battlefield, each player exiles the top of their library, then, Ragnar gains power and toughness becomes X, where X is the combined mana value of all cards exiled this way.
When Ragnar attacks, defending player sacrifices a nonland permanent they control, then, Ragnar gains power and toughness equal to the mana value of the card sacrificed this way.
When Ragnar dies, each opponent loses life equal to Ragnar's power.