Ill-Tempered Cyclops

• WWizards of the Coast2013-09-15
  Official Ruling
  Once a creature becomes monstrous, it can't become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
• WWizards of the Coast2013-09-15
  Official Ruling
  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.
• WWizards of the Coast2013-09-15
  Official Ruling
  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.

Rulings via Scryfall