It's called the Short-Lived Demo, and for good reason -- you can only play it between now and 7th October. There's also a special item to find while you play. Look for Dan's Helmet, an item previously exclusive to the Japanese version of the original, and you'll earn an extra challenge in the full game. Pretty cool.
Will you be checking out MediEvil's PS4 demo? Rise from your graves in the comments below.