Arbor Colossus | Magic: The Gathering
Formats Arbor Colossus is Legal in
Official Oracle Text for Arbor Colossus
: 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.
Official Rulings for Arbor Colossus
9/15/2013 : Monstrous isn’t an ability that a creature has. It’s just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.
9/15/2013 : An ability that triggers when a creature becomes monstrous won’t trigger if that creature isn’t on the battlefield when its monstrosity ability resolves.