First documented in the notes of the White Whistle Delver Lyza "The Annihilator", Ryuusazai are creatures resembling a horse with a long neck and what appears to be a beak. Their skin is covered in scales like a reptile and they have six long legs supporting their body. When it receives an impact, its scales will break off. Furthermore, these scales are laced with a dangerous poison. The end of their back holds a growth reminiscent of a snail shell.
Males often engage in fights with one other, tackling each other tenaciously ignoring the curse and moving in a three-dimensional manner. Their towering size, comparable to that of a large dinosaur, makes for an imposing figure and they are considerably strong creatures The danger level of a single Ryuusazai is said to equal to that of an entire swarm of Amaranthine-Deceptors. However they don't appear to be particularly aggressive, so if their territory isn't breached a safe passage is feasible even around their vicinity.
Just like the Silkfang and Inbyo, when its territory is breached, the Ryuusazai will tail and attack the intruder. When in close range, it uses its long rigid legs to stomp and impale the perpetrator. They are even able to chip the strong metal that makes up Reg's arm. When out of range, its proboscis-like appendage will open up and it will spit out a projectile, which appears to be a mixture of rocks and something slimy.
- One of the beasts of the Abyss that can damage Reg's body.