Several of those could only be found in the 5th Secret Realm.
However, the materials required to upgrade Bai Tianyu's two Guardian Beasts were much simpler.
Both the King Kong Beetle and the Nine Heavens Mysterious Turtle needed only five materials each to upgrade their Combat Power Level.
As for the Species Level, one required six kinds of materials, and the other needed seven.
Nevertheless, whether it's the materials for upgrading Combat Power Level or Species Level, they were all available on the internal platform of the Beast Trainer Association!
It's just that the total price was a bit high, causing Chen Fan some pain...
To upgrade the Combat Power Level and Species Level of these two Guardian Beasts by one level each, the materials would cost a total of 6.85 million union coins!
As expected...
Besides the high level of the Guardian Beasts requiring more valuable materials, the main reason was that their Potential Levels were too low.