Plague Doctor, Death's Decay

Wither.
Rats you control have wither.
Whenever a creature an opponent controls dies, if its toughness was less than 1, draw a card.

If one or more tokens would be created under your control, those tokens plus that many 1/1 black Rat creature tokens are created instead.
{b}, Sacrifice X Rats: Target Creature gets -X/-x until end of turn.
{u}, Sacrifice X Rats: Target player mills X cards.