The counters are added and then removed without a pause for priority or state-based actions being checked in between.
2005-06-01
All +1/+1 counters on Descendant of Masumaro are removed, including those put on it by other effects.
At the beginning of your upkeep, put a +1/+1 counter on this creature for each card in your hand, then remove a +1/+1 counter from this creature for each card in target opponent's hand.
Descendant of Masumaro’s printed power and toughness is 1/1, so removing all the +1/+1 counters usually doesn’t reduce the creature’s toughness to 0.
