How to Get Vault Keys in Sonic Frontiers
What are Vault Keys?
“A silver key with a hollowed out head shaped like the outline of a Chaos Emerald“. -In-game description.
Chaos Emerald Vault Key are a type of collectible item in Sonic Frontiers which are used to unlocking vaults that contains Chaos Emeralds and these keys are obtainable by completing missions and challenges around the Starfall Island. The keys will be available after completing a Cyber Space stage and once Sonic goes outside of it and returns to the Open Zone area.
Ways to Get Vault Keys
Obtained from clearing Cyber Space stage.
As it was mentioned above, it can only be rewarded after doing the challenges and you will receive a specific quantity of Vault Keys depending on the number of missions that were completed after clearing a Cyber Space stage.
You can also get an extra Vault Key in the Cyber Space when you collected all the Red Star Ring during a stage.
Tradable for 15 Treasure Token
The Chaos Emerald Vault Key is available for trade at the Fishing Spot where Big the Cat is located, you can exchange your 15 Treasure Tokens for a vault key and you can get treasure tokens by playing the fishing mini-game.