Mona Lisa

You can only attack with tapped creatures. Creatures you control at your upkeep that are untapped become tapped. Mana abilities that would usually tap creatures untap them instead. As long as you have 3 ore more tapped creatures on the battlefield, Mona Lisa gets +2/+1 and gains indestructible until end of turn.
{ut}{x} Mona Lisa deals X damage to up to Y target creatures, where Y is the amount of untapped creatures you control.