15 Sept 2013
If blockers have already been declared when Stoneshock Giant's last ability resolves, those blocks won't change or become undone.
15 Sept 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.
15 Sept 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.
15 Sept 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.
15 Sept 2013
Your opponents can't assign any creature without flying to block that turn, even if that creature had flying or wasn't on the battlefield under one of your opponent's control when Stoneshock Giant's ability resolved.