Monster Rancher, known as Monster Farm in Japan, is a multimedia series developed and published by Tecmo. The series began with the release of Monster Rancher for PlayStation on July 24, 1997. Players could acquire monsters by using real CDs. When a CD was inserted into the console, the game would use its metadata to create a new monster. The type of CD mostly didn't matter but there were a few fun Easter eggs such as Christmas albums would result in a "Santa" type monster and inserting the Tecmo's Deception: Invitation to Darkness game would result in Ardebaran becoming a playable monster.
I have wished for years that they would come out with a new version of this. It could be done in many different ways. They even found a way to do it with the GBA
The industry is moving to digital only on all platforms so doubt we’ll see something like this again. Maybe instead of a CD, using a photo or a sound? Something more generic and less reliant on physical media. The game itself has since been ported to modern platforms but without the CD gimmick.