About This Question
People wondered what you use Diamonds for in Best Fiends. You use diamonds to get keys and to level up fiends.
Diamonds Are Used to Buy Keys to Open Cages
You can buy keys with diamonds. You will be able to open more cages and get more rewards. The cost of opening the locks goes up as you progress in the game. You will need to spend more diamonds.
Diamonds Are Used to Level up Fiends
You use blue and yellow Meteormites to level up fiends. You will use these materials a lot and often you will not have enough of one to level up a fiend. I never have enough blue Meteormites.
You can use diamonds to cover the cost of the Meteormites you are missing. With enough diamonds, you can level fiends up by using them and no Meteormites. In most cases, I use them when I am missing some Meteormites.