Grimmsnarl is a green-skinned humanoid Pokémon mostly covered in long, dark purple hair, except for part of its face, its abdomen, its feet, and a small red patch on its chest. Most of its hair wraps around its body, except for a lock on each side of its face, a few spikes raised on its shoulders and some locks draping from behind its legs resembling a cape. While being bulkier than its pre-evolutions, Grimmsnarl is more slender than it appears to be, with its hair giving the appearance of a muscular body. Grimmsnarl's hair works like muscle fibers and helps enhance its strength. Grimmsnarl is able to move its hair, and uses them to ensnare opponents in a tentacle-like fashion. By using its hair in this way, Grimmsnarl is powerful enough to overwhelm Machamp.
Like its pre-evolutions, Grimmsnarl has tall, large crescent-shaped ears with red insides, as well as a long, sharp, upturned nose with a single long red nostril. It has a blue tongue and six teeth protruding from its mouth: two pairs of flat front teeth on each jaw, and a pair of sharp fangs on the upper jaw. It has white eyes with red irises, black pupils, and gray eyelids. Its face ends in a small pointy chin. Grimmsnarl's hands and feet have three pointed digits each. Grimmsnarl and its pre-evolutions are male-only species. It lives in the forests, and retains the troublemaking behavior of its pre-evolved forms.
While in its Gigantamax form, it becomes much taller and all of its body except its face and chest mark is covered in hair. Its limbs become longer, and its hair now makes up its hands and feet, each with three and two digits respectively. Its eyes are red with white pupils, and the hair from around its neck and shoulders is raised in a pointy collar shape surrounding its head, as the two longer rear locks join in a single spike waving above the head. Three red clouds surround the back hair that pointed up. When in Gigantamax form, it is capable of creating a powerful drill with its leg hair, which can bore large holes within Galar's terrain. Thanks to its increased strength, Gigantamax Grimmsnarl can jump over the world's tallest building. In Generation VIII, Spirit Break was one of its signature moves. In Generation IX, Confide is one of its signature moves.
Grimmsnarl and its pre-evolved form, Morgrem, are the only known Pokémon capable of learning the move False Surrender.
Gigantamax Grimmsnarl is the only known Pokémon capable of using the G-Max Move G-Max Snooze.
- No Pokémon have the same type combination as Grimmsnarl and its pre-evolved forms.
- Grimmsnarl, Hatterene, and their evolutionary families can be considered counterparts.
- Both are Generation VIII Pokémon evolving once at level 32, then at level 42.
- Grimmsnarl and its pre-evolved forms are male-only, while Hatterene and its pre-evolved forms are female-only.
- Each Pokémon in each evolutionary line has the same base stat total, base experience yield and catch rate as their counterpart (e.g. Grimmsnarl and Hatterene both have a base stat total of 510), except for Hatenna and Impidimp's catch rate.
- These two evolutionary lines are next to each other in the National Pokédex, the Galar Pokédex, the Crown Tundra Pokédex and the Paldea Pokédex.
- Both Pokémon are based on mythical beings from European folklore and mythology: Grimmsnarl resembles trolls, ogres, and goblins, and Hatterene resembles witches.
- Both Pokémon are Fairy-type Pokémon based around long hair that have their Speed drop upon evolution.
- Both Pokémon are the signature Pokémon of a rival in Pokémon Sword and Shield who is a succeeding Gym Leader and Gigantamaxes it (Marnie's Grimmsnarl and Bede's Hatterene).
- Grimmsnarl and its pre-evolved forms are the only Pokémon that are in the Fairy and Human-Like Egg Groups.
Grimmsnarl may be based on ogres, trolls, and potentially oni, all large and malevolent humanoid creatures from folklore and mythology that are commonly depicted with grotesque appearances and abundant hair. It may also be based on modern artwork of the Chimimōryō, a general term for monsters of the mountains and rivers, particularly of the large and hairy creatures. Like its pre-evolutions, Grimmsnarl also shares traits with goblins. The fact that its strength comes from its hair may be a reference to Samson from the Book of Judges.
Considering its association with Hatterene, Grimmsnarl may also be inspired by the bogeyman, bugbear, or coco, fictional creatures created throughout European cultures to frighten children that do not want to sleep or stay quiet. In addition, it resembles depictions of Grendel, a giant monster from the Old English epic poem Beowulf, described as a "creature of darkness" and known for his immense strength.
Grimmsnarl may be a combination of grim and snarl. The spelling of Grimm- may also indicate Grimmsnarl was named after the Brothers Grimm, a duo of brothers who traveled Europe gathering folklore and oral fairy-tales and cataloging them all into a singular book, Grimms' Fairy Tales. Its name could also incorporate the words gnarly, referring to its mangled appearance or unpleasant behavior; grimoire, a type of spellbook; Grímnismál, a mythological poem in the Poetic Edda; and grimace, a term for a twisted facial expression which Grimmsnarl bears.
Ohlonge may be a combination of ogre and ロン毛 ronge (long hair).