The PS4 remake of MediEvil has a secret bonus feature that if unlocked, allows you to play the original PS1 version of the game complete with its original graphics within the remake itself.
As reported by PowerPyx, the MediEvil PS4 version has a new set of collectables called "Lost Souls." Finding the 19 Lost Souls throughout the game and laying them to rest unlocks the PS1 version of the game. You can then find the PS1 Version in the main menu under Old Game.
In the Entrance Hall level, if you take the right path down the stairs, you'll find a blue chest that unlocks the Lost Souls. You'll then find the Lost Souls throughout the game who will give you a riddle. You will then need to put these souls to rest in other levels. There are 19 of these Lost Souls in total.
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