Muuns are stored and equipped in the "Muun Inventory" (hotkey: (L)).
There are "primary" and "secondary" equipment slots, allowing you to equip two Muuns simultaneously.
Only the Muun equipped in the "primary" slot will be displayed in the game.
When equipped, Muuns will gradually lose health. You can also choose which Muun to display (the hero Muun or the hero Muun).

Moon can be cured with the Jewel of Life!