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{4}{S}{S}: Monstrosity 2. (If this creature isn't monstrous, put two +1/+1 counters on it and it becomes monstrous. {S} can be paid with one mana from a snow source.)
As long as Chillerpillar is monstrous, it has flying.
Chillerpillar gaining flying after it becomes blocked won’t remove the blocking creature from combat or cause Chillerpillar to become unblocked.
Monstrous isn’t an ability that a creature has. It’s just something true about that creature. If the creature stops being a creature, loses its abilities, or loses its +1/+1 counters, it will continue to be monstrous.
Once a creature becomes monstrous, it can’t become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
