Sunless Empire

Sunless Empire enters the battlefield tapped.
{t}: add {b}{g}.
{b}{b}{t}: As an additional cost to activate this
ability, pay {x} where {x} is the mana value of
target creature you don't control with
a -1/-1 counter on it. That creature becomes a
Rat in addition to it's other types.
Gain control of it, it gains infect.