Today I've added some things that polish the game a little more, mostly details, not many features.

Here is the video of the progress:

As you can see I've added a little story when the game begins.
Now, the wizard's name is Gabriel. :)
I've added a new type of grave that can give you skulls but it can also get skulls from you. It's your choice what you decide to do.
I've also added some new sounds (when the player collects skulls and when the wizard appears). In the video is not very obviously.
I've added a basic GAME OVER screen.
And the last thing I've implemented is the score tracker.

Tomorrow I plan to add a score saver and some more animations, maybe some new sounds...