Breath Of The Elderwrym

({p/r} can be paid with any amount of {r})
Rend {p/r}{p/r}{p/r}{p/r} (you may cast this for it's rend cost if you control a dragon)
Breath Of The Elderwrym deals X damage to all permanents with health you don't control, where X is the amount of mana spent to cast Breath Of The Elderwrym. If Rend cost
was paid, double the damage