Hydra Shop becomes available once you unlock Elemental Cradle at team level 35. You can access the Shop by tapping Merchant in the Elemental Cradle menu:
You can also select the Hydra Shop tab when you open any other Shop:
At Hydra Shop, you can purchase Yasmine and Morrigan Soul Stones, Elemental Spheres, chests with hero artifact resources, Artifact Coins, Sparks of Power, Chaos Cores, and gold. Items in the shop do not change.
The goods reappear every 24 hours at 9:00 PM your in-game time. You can also refresh the Shop using emeralds.
Note
To get more Hydra Coins, exchange extra titan artifact fragments in your Inventory. Exchange rate: 1 fragment = 2 Hydra Coins.