At the beginning of your upkeep, each player exiles the top card of his or her library, then flips a coin. For each player whose coin comes up heads, that player may play a card he or she owns exiled with Magmatic Rumblings without paying its mana cost.
For Challenge # 082.
Ooh. An unpredictable Omen Machine. Yeah, this doesn't appeal to as many players as Omen Machine, but I could still see it getting printed at some point.