Medic

Toughness is determined by the amount of creatures on the battlefield that you control with the subtype 'Human Mercenary'. If you control one or fewer, Toughness is 2.
{w}{w}{r}{r}{r}{g}{e}{e}, {t}: Medic and one other card with the subtype 'Human Mercenary' are invulnerable for two turns and gain 'Defender' in addition to their other effects for two turns.
"Oops, zat was not medicine!"