Creature â Giant
: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Arbor Colossus becomes monstrous, destroy target creature with flying an opponent controls.
Once a creature becomes monstrous, it canâ€™t become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
Monstrous isnâ€™t an ability that a creature has. Itâ€™s just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.
An ability that triggers when a creature becomes monstrous wonâ€™t trigger if that creature isnâ€™t on the battlefield when its monstrosity ability resolves.