The term "Hellboy pepper" refers to a couple of things: a specific, very hot pepper variety used in hot sauces, and a line of hot sauces named after the Hellboy comic book character. The pepper variety, "Hellboy," is a cross between the Big Black Mama and Chocolate Moruga Brains peppers, known for its intense heat and dark chocolate-brown color when ripe. The hot sauces, like Hellboy Legendary AF and Hellboy Right Hand of Doom, utilize this pepper along with other superhots and are known for their extreme heat, some even using pepper extracts. 
Pepper Variety:
The "Hellboy" pepper is a crossbreed developed by Lucas C from Joker Chilli. 
It's known for its dark chocolate-brown, wrinkled pods that start green. 
It's a Chinense variety, meaning it has a typical Chinense pepper flavor. 
The pods are 4-5cm long and 3cm wide. 
The plant grows to about 1 meter tall and 0.75 meters wide. 
It's considered extremely hot and not for the faint of heart