Prophet of Pestilence

Whenever a creature you don't control dies as a
result of having its toughness reduced to less than
1, you may put a -1/-1 counter on target creature.
{2}, Sacrifice a creature: Target creature gets
-2/-2 until end of turn.
"The illness is highly contagious. Transmission occurs
via aerosol, water and physical contact."
—Phyrexian progress notes