Feud of Foes

At the beginning of each upkeep, each player
reveals the top card of their library and puts it on
the bottom of their library. Each player who
revealed a card this way may have Feud of Foes
deal damage equal to the converted mana cost of
the revealed card to any target.
At the beginning of your end step, if no damage
was dealt since your last turn, shuffle Feud of
Foes into your library.