Adding them to hard difficulty is nice idea for anyone looking for more challenge without affecting experience of casual player.
I am saving those 4P and 5P animation for goblin only level.
I would add that the only room that has 2 goblins in it has the goblins in water, so if they do get you, the animation is slightly obscured due to the swampy water goo stuff. Might be worth considering that when talking placement, but I can't stress enough how nit picky this note is. Like, that and the red skeleton at the top of a rope that makes it hard to get off the rope, are the absolute only two things that weren't awesome imo.