Riddle

Riddle doesn't untap during your untap
step
{b}{t}: Target player discards a card.
{g}{t}: Add {b/g}
{b}{g}: Only activate this ability if Riddle is
tapped. Destroy target creature. You can only activate this ability once per turn.
{b/g}{b/g}{b/g}{b/g}: Untap Riddle.