Traits

[Potion item]: Magic Eclair

A tail that is longer than the leech's body.   Visual Reference Guide

While some tails are longer than others, typically a leech's tail is only as long as its body. This odd mutation caused it to grow up to three times the body length. 
Longer tails have been recorded, but they are very easily damaged and tend to have reduced mobility, especially in the wild where it can be caught or attacked easily.