Use the creature's power as Madame Null's last ability resolves to determine how much life you may pay. If that creature is no longer on the battlefield, use its power as it last existed on the battlefield. (You probably won't want to pay life in that case, though.)
Deathtouch
Whenever another creature you control enters, you may pay life equal to its power. If you do, put that many +1/+1 counters on it.
