The recommended use of Jewels is to buy the special buildings that help with Archwitch encounters: the Magic School, which increases the encounter rate of Archwitches, and Yggdrasil, which increases the maximum battle points (required to battle Archwitches). These special buildings cost  Jewels each.
Other things you can do with jewels are:
- Recovering your cards without using any resources.
- Performing premium summons (summon for  Jewels each or  Jewels for 10+1 premium cards).
- Buying recovery items or deck expansion items.
- Buying jewel-exclusive decorative buildings.
- Buying resources for one of the 4 resources types. You can choose from 10%, 50% and 100%.
- Finish buildings in an instant.
- Resetting the duel timer to 00:00.
- Unlocking additional pages of your displayable collection for  Jewels per page (maximum 45).
- Increasing Deck Cost.
- Upgrading Resource buildings from 10 to 11 for  each.
Obtaining Free JewelsEdit
Jewels can be obtained from area rewards, quest rewards, login bonuses, during World of the Gods Slots events (as a prize of 5 or 100), Collaboration Rewards, Tapjoy rewards (in Summon page under Free Jewels!), or sometimes as gifts from the devs. They cannot be found from advancing through areas and Archwitches do not hold jewels as rewards.
It is important to carefully manage your free jewels. It is not recommended to spend free jewels on summons early in the game, since the rate of obtaining a useful SR or UR card is very low.
The current prices for jewels (taken from the official in-app prices) are:
You can also purchase jewels for yourself or others using the GASH system on Nubee's website that is still maintained be MyNet. The price per jewel is slightly less than purchasing directly in game.