After clearing all sixteen Challenges in a World (the normal run plus all three Challenges of each of the four Levels) go and talk to the King. He will give you a Gold Rank Material for that World which can otherwise only be obtained from the Colosseum. It doesn't matter if the Challenges were cleared in Multiplayer or Solo Mode, as long as all sixteen Triangles are lit up on the Board. You can only receive 1 of each Material from the King.

Unlockable	How to unlock
1. Supple Leaf	Clear all Challenges in Woodlands.
2. Thornberry	Clear all Challenges in Riverside.
3. Divine Whiskers	Clear all Challenges in Volcano.
4. Beastie Patch	Clear all Challenges in Ice Cavern.
5. Brittle Papyrus	Clear all Challenges in Fortress.
6. Golden Insect	Clear all Challenges in The Dunes.
7. Gold Dust	Clear all Challenges in The Ruins.
8. Fabled Butterfly	Clear all Challenges in Sky Realm.