Ghast Ouster

{1}{u}: Halve target creature's power until end of turn. (Round down.)
{1}{g}: Double target creature's toughness until end of turn. Activate this only once per turn.
{2}{b}: Ghast Ouster gains lifelink.
{2}{r}: Name a creature type. Ghast Ouster deals 1 damage to each creature with that type and each Cleric.