The Lygirosaur can grow to a size equal to the mass of a Death Stalker. Its body is a cross between a gorilla and a velociraptor, in a sense that it looks like a raptor in almost every way, but it has gorilla-like qualities such as long forelimbs and a hunched stance with its forelimbs close to the ground. It is technically a biped, but, like a gorilla, it will often use all four limbs to run faster. Standing upright, it towers at roughly 15 ft; in its normal hunched stance, about 9 ft. It has all the typical Grimm characteristics with a few exceptions: it has no eyes in its mask, the spinal bone structure extends to its tail (which is the length of its abdomen) and is widest at the lower back, while it narrows up to its mask and down its tail. It has black scales, a soft white underbelly that goes down to the tail, three white bone claws on each hand (thumb and two fingers) and each foot (three front claws), and long white bone spikes protruding from the forearms out the elbows, about equal to the length of the forearms themselves, as well as bone spikes protruding from the heels, equal to the length of each foot. Its mask covers the top half of its long raptor head and extends into three long bone spikes at the crown of its head equal to its length. It has a large, expandable chest to accomodate its special ability.
- Strengths: It is incredibly strong and fast, able to topple trees twice its size. It uses its arm's protruding bone spikes as an offense against large enemies like Ursas or Nevermores, while its heel spikes are a defense against enemies attacking form behind. It has strong jaws, as well as a strong tail it uses to strike opponents from a distance. Its special ability is being able to inflate its single huge lung in its expanding chest and let out an incredibly loud roar not unlike a T-Rex that can last for several seconds and can even rupture human eardrums and kill small birds.
- Weaknesses: It is blind, having no eyes, so its uses scent and hearing to detect enemies and uses its long limbs to navigate, feeling around for obstacles. Its underbelly is its major weak spot, with huge gaps between its ribs and skin only as tough as leather. It also has to be stationary to use its roar attack at its full power.
- It is incredibly territorial and a loner, so it will assault any creature it considers a threat, even another Lygirosaur, as well as killing any pre-existing creatures in an area it decides to claim as its own.
- It normally resides in thin forests with tall trees. Its territory is often marked by stripped carcasses and felled trees, making shelter out of stacked trees like a fort.
- It will often topple trees using headbutts, feeling around for a tree at first, then budging it to test its looseness, and finally taking several steps back and charging at the tree.
- It hunts daily and only eats meat, so it will attack other Grimm for food as well.
- Its name comes from the word Lygirophobia, the fear of loud noises. This is an apt name for the Grimm, since its roar is easily fear-inducing.