When Disciple of Phenax enters the battlefield, target player reveals a number of cards from their hand equal to your devotion to black. You choose one of them. That player discards that card. (Eachin the mana costs of permanents you control counts toward your devotion to black.)
9/15/2013 Use your devotion to black as the triggered ability resolves to determine how many cards will be revealed. If Disciple of Phenax is still on the battlefield at that time, its mana cost will count toward your devotion to black.
9/15/2013 Numeric mana symbols (, , and so on) in mana costs of permanents you control don’t count toward your devotion to any color.
9/15/2013 Mana symbols in the text boxes of permanents you control don’t count toward your devotion to any color.
9/15/2013 Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
9/15/2013 If an activated ability or triggered ability has an effect that depends on your devotion to a color, you count the number of mana symbols of that color among the mana costs of permanents you control as the ability resolves. The permanent with that ability will be counted if it’s still on the battlefield at that time.