The Great Snake Demon is a demonic summon that Melona used to attack Leina and the others at the Gainos Bridge.
Disregarding her large size, (and that she has no legs) The summon has the appearance of an attractive woman, who looks more mature than the other characters in queen's blade. She has three long horns attached to her head. One points forwards, coming from her forehead, comparable to a Unicorn's horn, and the other two come straight out the side of her head, comparable to a very typical western demon fashion. Her hair is light violet, and is wavy and long, ending right after the middle of her chest. Her skin is purple, and she has light purple shoulder guards, with orange spikes coming out of the side. Her breasts are not covered, but she wears an off side purple plated skirt and has a large circular shield attached to her arm, as well as a light purple sword, that looks very similar (except for the color) to Leina's sword. However, instead of legs, she has a lizard-like sea-monster tail, which is once again, purple with golden spikes, that seems to be very long. Her eyes are golden, and slitted like a snake or cats eye. She has long, sharp dark purple fingernails on her hands, as well as some strange purple bandages wrapped around her arm.
The summon has a huge sword (although normal sized for her height), and is shown to very powerful-in one hit, as she causes Airi to de-materalize. She also can crush the ground with her sword, showing her great strength. Her great size and tremendous strength makes her very intimidating, and extremely difficult to fight.
Ymir is scared of the entity, because it looks similar to a snake, and she runs away and can't fight it.