Demonius Rex, God of saurs

God of extinction
Whenever Demonius Rex attacks, the rest of the opponent cards will take 3 damage if you spend two extra r/b mana. If attacking the opponent, Demonius rex will only do 12 damage instead of 20. Unless there are no cards summoned by the opponent on the battlefield, Demonius rex can't attack the opponent.
"In our culture we've always seen the demonius rex as the god of extinction, an unbelievable large immortal dinosaur made up of every other archosaur."
—Thronaxak, dinosau