Loose-Lipped Merchant

Cumulative upkeep - Exile the top card of your library face-down. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever you exile the top card of your library face-down, until end of turn, target opponent may cast that card as though it had flash and may spend mana as though it were mana of any color to cast that spell.