Mullo is a small mouse-like creature with gray ears, her eyes are pink.
Like all kwamis, Mullo can fly, levitate, phase through solid objects, and carry things that are bigger than her.
Mullo can transform the holder of her Miraculous into a mouse-themed superhero by going inside their Miraculous.
As a kwami, Mullo gives the wearer the power and transforms them into a mouse-themed superhero by entering the Mouse Miraculous. Although unable to communicate to the wearer while they are transformed, Mullo usually knows what is going on during that time. Whenever the wearer uses Multitude, Mullo begins losing power and eventually can't retain the transformation any longer, leaving the pendant necklace and reverting the wearer back to normal. Mullo is exhausted and out of energy afterwards, so to be able to transform the wearer again, it must refuel by eating food.
Thousands of years prior to the series, Mullo and the other Kwamis traveled the universe, unable to interact with any creatures, particularly humans. This was until a mage forged the Miraculouses, so Mullo and the others could both interact with mankind and grant them the ability to transform into heroes; Mullo and the Mouse Miraculous able to give a person the ability to grant other people superpowers.
In "Kwamibuster," she temporarily uses the Mouse Miraculous to become "Multimouse" and becomes many forms like "Multifox," the fusion form of Marinette with both the Mouse and Fox Miraculous, "Multicat," the fusion form of Marinette with both the Mouse and Cat Miraculous, & "Multibug," the fusion form of Marinette with both the Mouse and Ladybug Miraculous, Master Fu remarks on how exceptionally, physically and mentally strong Marinette is to have used so many Miraculouses at once.
She will habitually enable Mylene to transform into a mouse-themed superheroine during season 4.
- Mullo is the kwami of Multiplication.