The Doom of Djeruba

Prophecy (When you draw this, you may exile it
face up. At the beginning of your upkeep, if it's exiled
this way, put a prophecy counter on it. You may cast
it for as long as it remains exiled, and it costs {1} less
for each prophecy counter on it.)
Each nonland permanent becomes a land with
"{t}: Add three mana of a color in this
permanent's color identity" and loses all other
card types and abilities.
Players take 1 damage for each unspent mana at
the end of each phase for the rest