Détecteur longue portée

Whenever you attack a player, put a charge counter on this artifact. {1}, Remove two charge counters from this artifact: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)