This is a beast Egg. It's pretty useless until it hatches.In-game description
The Hellfire Egg is a black egg with a set of vertical red streaks coming down from the top. Based on the sprite, there is also a small streak on the bottom.
Hellfire Eggs cannot be found in the wild. They are not used by any enemy signers, even those participating in the Random Tournament.
This egg will hatch into a Hob.