Or were you looking for Mad Endo's stronger counterparts, Overclock or Gold Endo?
Mad Endo is a boss encountered in FNaF World. They're encountered in Deep-Metal Mine and Choppy's Woods. They stand guard to variousgoldenand redchests.
Mad Endo's appearance is almost identical to Endo-02's appearance, minus the skeleton-like head and the strange two-toed feet. Its body seems to be merged together, giving it a strange look. It is noticeable that if one looks closely, it has sharp claws. Overclock and Gold Endo have them as well, due to being just a powered-up version with nothing changing in appearance and a recolor, respectively.
However, one of them appears in Choppy's Woods, only to guard the chest that holds the Pizza: Fury chip.
Mad Endo is one of the five bosses that are considered optional bosses, since the player doesn't need to defeat it to complete the story. The other four being Auto Chipper, Eyesore, Seagoon and Gold Endo.
Mad Endo is the only boss that has the Gloom attack.
It is possible that Mad Endo is the endoskeleton for Porkpatch and Bubba, though this is unconfirmed.