An Ominous Trial Key is a special variant of the Trial Key used to unlock Ominous Vaults inside Trial Chambers. Unlike regular Trial Keys, which open standard vaults, Ominous Trial Keys grant access to higher-tier loot. To obtain an Ominous Trial Key, a player must complete a Trial Spawner challenge after entering the Trial Chamber with the Bad Omen effect, which is gained by drinking an Ominous Bottle.
This makes Ominous Trial Keys more difficult to acquire, as players must first find an Ominous Bottle, obtain Bad Omen, and then successfully clear a Trial Spawner. Ominous Vaults may contain stronger or rarer rewards, making these keys worth the extra steps for players exploring Trial Chambers.