The original Ghoulghilas was made by Akane to get revenge on Tonkawa for knocking down the special dog she was giving Yuta, and another is Mecha-Ghoulghilas (メカグールギラス, Mecha Gūrugirasu), an upgraded version which was used to ruin the school festival as means to lure Gridman out to destroy him once and for all.
Ghoulghilas is a large, reptile-like kaiju with a red and blue color scheme. Its underbelly is mostly a light red, with a blue back. It has two legs and two arms, both with long nails. It also has a long tail with white wire-like parts at the end. It has a long neck that portrudes sideways, and its head has two backward-facing horns. It has a large mouth filled with uneven teeth, and red eyes. Its spine is covered with spikes, the most large of which are on its back. The blue parts of its skin are rough and bumpy.
Like most kaiju, after being sliced open, its insides are revealed to be multicolored wires and circuits.
Mecha-Ghoulghilas basically resembles the original, but the entirety of its body is teal green while the hands, head, and neck are replaced with robotic ones. Robotic, segmented armor plates can be seen adhered on the leg and spine, with the end of the tail having a drill on it. It also carry a large armor plating with built-in cannons and what appeared to be sensors on them. The inside of its mouth has twin barrels from which it fires its fiery beam.
Ghoulghilas has basic strength, speed, and durability of a kaiju in its size. Its primary means of attack is the ability to fire bursts of fireballs from its mouth. The fireballs possess enough firepower to decimate an entire building in one shot, or to stagger Gridman. The fireballs also bounce off the ground for additional distance rather than exploding immediately.
A flaw in Ghoulghilas' physiology is its fragile neck, as it ended up decapitated by Gridman with a single slam. Even so, it survived for a while after having its head removed, stripped it of its ability to project fireballs, although how long it can live without its head is uncertain, as Gridman immediately destroyed it afterwards.
Unlike its predecessor, Mecha-Ghoulghilas is designed as one-man army, as its combat capabilities greatly enhanced and even has its flaws rectified. While still capable of survive from being beheaded, it can survive much longer and not discomforted at all thanks to presence of sensors on its upper back.
Other than armor plates, Mecha-Ghoulghilas is armed with an array of weaponry:
- Plasma Flamethrower: Mecha-Ghoulghilas has built-in Plasma Flamethrower in its mouth that can fire a continuous stream of fire. While its firepower enhanced that it can suggestively punches its way through multiple buildings, it is not strong enough to breach Full-Powered Gridman's armor.
- Blaster Turrents: Mecha-Ghoulgilas has a pair of blaster turrets installed on its back.
- Drill Head: The armored plates on the sides of its head can close up to form a drill, and the entire head and neck spins at a high speed. While supposedly destructive agianst most defenses, it is not strong enough to make a dent on Full-Powered Gridman's armor.
- Tail Drill: Mecha Ghoulghilas has a drill on its tail, though how good its destructive capabilities never shown due to overwhelmed by Full-Powered Gridman.
Ghoulghilas is the first kaiju to appear. One of its fireballs bounced and hit the school, killing Tonkawa, Toiko, and at least three other people. Gridman defeated it by going for its neck, which Sho found to be the weak spot and Rikka communicated about with Yuta.