Mummy Sandbox? Where?...It's on the Haunted PS1 Demo Disc 2021! Go play it now!
Additionally, if you want more madness, check these bizarro platformers & experiences around 20-30 minutes! The Meanderthal #1 & The Red Mummy intermix games & comic books in a unique way. I also have a habit of really glitching out Battletoads!