Find an Ancient City in the Deep Dark biome
Locate a Trial Chamber
Open Ominous Vaults
Use an Ominous Trial Key to unlock an Ominous Vault
Collect the Heavy Core from the Ominous Vault loot
Repeat Trial Chambers and Ominous Vaults if needed
Find an Ancient City in the Deep Dark biome
Locate a Trial Chamber
Open Ominous Vaults
Use an Ominous Trial Key to unlock an Ominous Vault
Collect the Heavy Core from the Ominous Vault loot
Repeat Trial Chambers and Ominous Vaults if needed