2017-04-18 : If a creature with wither or infect deals damage to a creature, the controller of the creature with wither or infect puts that many -1/-1 counters on the second creature.

2017-04-18 : If an effect has you put more -1/-1 counters on a creature than it has toughness, you’ll put all of those counters on it and create that many Insects, even if that makes its toughness a negative number.