Dungeons!

Dungons are the areas in the game that you will explore to gain your items and progress further, and you guessed, you can fuse dungeons together

when you start the game you will be able to select one location, the crypts, but you can unlock more at the shop and fuse them together. perhaps theres a location called "The Mines" and "The Forest" and when you fuse it together you gain access to "The Gilded Forest." and the enimes would get fused together as well, perhaps there is a Golden Golem in the mines, and Dryads in The Forest, and when you fuse it together you would end up encountering "The Gilded Dryad"