Horrors are small, adorable but extremely lethal dragons seen in The Incomplete Book of Dragons.
Horrors are devious little dragons are very cute by human sensibilities, but can kill a human many different ways. They are shown to be bright yellowing-orange in color, possibly to indicate its poisonous nature.
Horrors are listed as Sea Dragons, so they are assumed to spend a large amount of time in or around the sea or ocean.
Horrors can produce electric shocks or lightning bolts (its unclear which), have acidic blood, create toxic gases that can render a human unconscious, and are poisonous. On top of that Horrors have X-ray vision, hypnotic powers, and are one of the very few dragons that can see into the future.
Horrors are described in this reference book and are listed in the Dragon Key Table at the back of the book.