To give the keys a fresh look and more value, I came up with the idea of ​​adding a marketplace focused on them. In dungeons alone, there will be a 20% chance of receiving 2 to 10 dungeon gems. These can be exchanged with the dungeon merchant, who has a 35% chance of appearing at the key's entrance every hour. When they appear, there will be a button to notify your guild, friends, or the server. They will sell various items:

 

Detector Scroll (10): Tells you the number of players on the level.

 Chest Key (100): Allows you to recover 1 lost chest (only stacks with a keyring).

 Dungeon Potion (50): Increases the gem drop rate to 30% for 1 hour.

 I also came up with the idea of ​​adding an inventory slot for passive buff items like Death Charms, and new items that will be sold:

 1. Aggression Core (500): Grants 40 Aggression and 5 Defense.

 2. Fairy Flask (400): Each time you take damage, your Mana Regeneration increases. 

3. Brass Knuckles (500): When attacking a tile directly around you, you gain a second attack with reduced damage. 

I had considered making these three items usable only by one class: Archer = 1, Mage = 2, or Knight = 3. In that case, all three would cost 500, and items and dungeon gems would not be transferable. Although I believe the future grimoire will have the Fairy Flask effect, since I don't know its usefulness, I decided to use whatever is available.

Dungeon Merchant + extra slot