Traits

 Once highly sought after for ornamental and regal leeches, oni teeth are now considered a defective trait where a leech monster will grow an extra tooth on each side of the upper jaw that curves outward and to the sides, preventing them from easily biting their prey. 

Leeches with these teeth often have to turn to unconventional food sources or develop other traits in order to compensate for the oni teeth, and its mythical classification is based on the heightened intelligence and adaptive mutations that accompany this leech as it struggles to feed.  Oni teeth are considered bad luck, and the superstitious would rather pelt the leech in question before it develops an ability that could harm and kill them.

Note: This leech still has teeth plates in part and should be illustrated as such, though the extra teeth are often standalone set individually into the gum.