Each beast has a star level. 1 is the lowest and 3 is the highest.
2-star beasts are evolved from fusing three of the same 1-star beasts
3-star beasts are evolved from fusing three of the same 2-star beasts
All beast hunters have a Dexicon (just like a Pokédex). There are 151 unique beasts. Beast hunters can complete their Dexicons by collecting all #1-#150 beasts. By completing the Dexicon, a beast hunter can claim the #151 legendary beast.