The Chaos Hound is a very rare mount that can only be found rarely in Chaos Chests. It resembles a form of corrupted pemblock, with some fish-like features.
As new Chaos Loot has been added, including items such Koroki, the Sower of Chaos, the Chaos Hound has been removed from the Chaos Chests. This makes the mount currently unobtainable, but it will later be reimplemented.
This Mount was designed by Forum user and Mod Maker, Aviarel. Here is the original post: link
In the original Forum post, it was called the Shadow Angler Pemblock.