Morelull is a small, white Pokémon similar to a mushroom. It has large, black eyes with pale green half-circle markings on the outer side. Small bumps ring the top of its head, similar to hair. Its head is much larger than its thin, stem-like body. At the base, the stem splits into three green roots that act as feet. Three large mushrooms sprout from the center of its head. Each mushroom has a thin white stem and a darker ring of color around the base of the cap. The center and largest mushroom is light pink, while the other two mushrooms are smaller and a light purplish-blue. At night, Morelull can make the spores filling their mushroom caps glow with blue light.
A nocturnal Pokémon, Morelull moves every night to a new location. It likes dark damp areas, but moves around to avoid depriving the plants in any one area of too many nutrients. In addition to locomotion, its roots are also used to make communicate with other Morelull. When in danger, it scatters spores that burst into bright, glittering sparks. The pulsing light of the spores can induce drowsiness. It is rumored that once, when a group of Morelull were disturbed and all threw out their spores at once, a plane passing overhead suffered a near brush with disaster.
Morelull can be seen as a counterpart to Paras. Both share the Grass type and the same base stat totals, both can learn Spore, and both can be found in the wild in Pokémon Sun and Moon, taking the place of the other depending on the time, with Morelull being found during the night and Paras at day.
Morelull may be based on bioluminescent mushrooms such as those of the genus Mycena, although its name suggests inspiration from the genus Morchella. Its Fairy type may be due to fairy rings, or it may possibly be a reference to fairy fire.
Given that some of the foreign names of its evolution include the word "lamp", and that Morelull shine lights and put people to sleep, it may also be based on a nightlight.