There are 5 types of Crystals in the game (Metal, Poison, Ice, Fire, Magic), used (along with coins) for Upgrading heroes of that element type
Obtained from:
In Runs:
- Kills in Castle (improved by Crafter) and weekday Daily events - although described as matching the event (e.g. Fire Crystals from Fire event / castle) in practice all crystals drop in all Castles/events
- Hidden Treasures
- Jackbot’s Jackpot
Outside Runs:
- One time rewards in Daily events
- Summon Gates
- BattlePass (including Rainbow Crystals that can be used for any hero)
Note: Please let me know if I’ve missed any uses / earning options