Key
From SpiralKnights
A Key is a type of arsenal item that can be used to unlock locked containers or areas. The key section doesn't show up in the arsenal if the player doesn't own any keys. Keys are obtained unbound.
Silver Key
A special key that can open any lockbox. Once used, the key is destroyed.
Silver Keys can be acquired from the Supply Depot for 750 energy. Each key can open one of any type of Lockbox.
Shadow Key
A mysterious key that grants a party access to Shadow Lairs. A Shadow Key is destroyed once used.
Shadow Keys can be acquired from the Supply Depot for 1800 CE each. Rarely, they can be unboxed from 
Iron Lockbox as well as 
Radiant Forge Prize Box. Only one is needed per party to unlock the Shadow Lair elevator.
Slime Key
A slippery key that can only open a Slime Lockbox. Once used, the key is destroyed.
Slime Keys can be acquired from the NPC Smitty when Golden Slime Casinos appear in the Clockworks. Each key can open one 
Slime Lockbox. Slime Keys can also be acquired from Gracken in Emberlight, for only 60kcr.
Notes
There are two types of keys that a player can have in the "Keys" section of the Arsenal.
The Gold Key object found in the Clockworks does not go into the player's arsenal. It is an object encountered in the field that simply serves as a means to progress through areas, similar to heavy statues and switches.
The 
Book of Dark Rituals and 
Fiendish ID Card are very similar to a Shadow Key in fuction. Each can only be used once per activity. To repeat the activity, another must be acquired. A single one can allow access for up to 4 players in the party. These items are stored in the material section of the player's arsenal.
