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Prevent the next X damage that would be dealt to target creature this turn. For each 1 damage prevented this way, put a +1/+1 counter on that creature.
The +1/+1 counters do show up at the same time as any unprevented damage, which means they are there before you check for lethal damage.
You can make X be larger than the amount of damage, but you only get one counter for each actual point of damage prevented.
