Haunter, The Gas Ghost

Flying, protection from green and colorless
{1}{u}, {t}: Tap target creature. It doesn't untap during its controller's next untap step.
{2}{b}, {t}: Put a -1/-1 counter onto target tapped creature and put a +1/+1 counter onto Haunter.
{3}{b}, {t}: Haunter deals 3 damage to target creature. Put a -1/-1 counter on it.
{4}{b}, {t}: At the beginning of target player's next untap step, they lose 1 life for each tapped creature they control.