Arbor Colossus

Text:

Reach
: 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.

Rulings:

• 9/15/2013 Once a creature becomes monstrous, it can’t become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
• 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.