There are a lot of different Cameo Quests, or Secret Levels, in Funko Fusion, and finding them can be a little tricky. Whether its just hard to find or if you just need a particular character to unlock it, players will have to do some searching to get to these Secret Levels. Once found, even more unlockables are hidden in these worlds to get your collectible senses tingling.
https://screenrant.com/funko-fusion-how-to-unlock-back-future-level/