You actually just fuse different animals with no currency or any major restrictions. The only limiter is that not all of them are unlocked, but you get a free one every 3 hours. Which considering the many other predatory means of implementing this mechanic (crazy IAP's, watching dumb ads, etcetera) is very fair and acceptable. This timer mechanic gives me something to come back to once I've exhausted the provided fusions, as adding one more monster compounds the number of available fusions. Additionally, the developer took the time to come up with an abundance of lore and statistics for EACH fusion, which adds significant depth to the app. If you enjoy gachas, monster collecters, and beastiarys of the sort then this game is gold.