Usable

Left-click on an upgrade to get the menu to use it.

A variety of usables are available in Spiral Knights, usually purchasable at the cost of energy.

Note that, after obtaining a usable, you must activate it to gain its benefits. You can do so by locating it in your arsenal, under the Usable section, left-clicking on it, and selecting "Activate" or "Upgrade".

Upgrades

Trinket Slot Upgrade

Trinkets are a type of gear that bestow a variety of small, but useful benefits to your knight. Any player can acquire trinkets, but in order to equip them, trinket slots must be unlocked with an upgrade. Up to two Trinket Slot Upgrades may be activated at a time. Each one will unlock a single trinket slot for 30 calendar days. An activated slot upgrade will remain visible in your arsenal with the expiration date and time showing in the mouseover tooltip.

Weapon Slot Upgrade

By default, players are only able to equip two weapons when they descend into the Clockworks. This limit can be increased up to four weapons by purchasing and using Weapon Slot Upgrades. Up to two Weapon Slot Upgrades may be activated at a time. Each one enables an additional weapon slot for 30 calendar days. An activated slot upgrade will remain visible in your arsenal with the expiration date and time showing in the mouseover tooltip.

Vendors

Upgrades can be purchased from Boost, located in the Bazaar section of Haven.

Other Usables

Mist Tank

Activating a Mist Tank completely fills up a knight's mist energy and removes a mist tank from your arsenal. Mist tanks are sent to knights by Spiral HQ via mail after achieving certain accomplishments and must be "Accepted" to be added to your arsenal from the mail. Mist Tanks will not allow a knight to have more than 100 mist energy.