Another day has passed (In Romania, right now is 10 pm).. and here it is my progress:

Now my game follows the theme shadows as a shadow catches the skulls to make my job harder.
I've added a background and some grass to make the scene look more like a cemetery.
I've also added a wizard which appears every 40 seconds and which gives you 3 skulls once you reach him. He cannot be eaten by the shadow, but It stays active just 10 seconds, after that, he disappears.

Tomorrow I'm planning to add another type a of grave (a bonus one) and also I want to work some more on the background and sounds.