Kung Pow! Enter the Fist

A man, called The Chosen One by the narrator, wanders from town to town to search for the man who killed his family and tried to kill him when he was a baby. In one town, he meets Master Tang, a very ill and slightly deranged sifu, and asks Tang to help him improve his already impressive martial arts ability. Master Tang is skeptical at first, but after seeing The Chosen One's mark (his sentient tongue, which he names Tonguey), he allows him to train at his dojo. The Chosen One is introduced to two other students: Wimp Lo, a young man who was deliberately trained incorrectly as a joke, and Ling, who has feelings for him.
While training, The Chosen One shows cartoon-like feats of strength, and Wimp Lo deems him an enemy out of jealousy. Upon learning that Master Pain, the man who killed his parents, has just arrived in town, The Chosen One prepares to confront him. Master Pain draws a crowd and demonstrates his skills. He lets his henchmen kick him repeatedly in the groin, then subdues them all in one move. Impressed by Master Pain's skills, the town's mayor hires him, and he randomly changes his name to Betty. The Chosen One attempts to train himself by letting people kick him in the groin, but is knocked out after being hit. When he wakes up, a mysterious woman named Whoa warns him not to rush to fight Betty. After flirtily fighting The Chosen One, Whoa flies off into the sky.
Ignoring the advice, The Chosen One sets off to find Betty. He comes across one of Betty's evil companions: Moo Nieu (pronounced "moon you"), a Holstein cow gifted in karate, with a large udder that can squirt milk as a weapon. They fight in a scene parodying The Matrix, and The Chosen One eventually incapacitates Moo Nieu by milking her until her udder is empty. He sees Betty at a waterfall and confronts him. Master Doe, Ling's Father, shows up and tries to stop the unprepared Chosen One, and is wounded by Betty. The Chosen One takes Master Doe to Master Tang; it turns out they are old friends. However, as Tang massages Doe's wound, it doesn't close and Doe dies that night. Out of depression, Ling confesses her feelings for The Chosen One.
Confused, The Chosen One journeys out to a field and consults the heavens for confidence. Suddenly Mu-Shu Fasa, a large sentient lion, appears in the sky and dispenses advice in a scene parodying a portion of The Lion King. He returns to town and finds that Betty's hostility has expanded to the entire town, and they are killing anyone who may be his allies. He finds Wimp Lo, Ling, Master Tang and even his Dog heavily maimed. However, except for Lo, they all survive. After taking Ling and his dog to safety, The Chosen One begins training himself. Believing Betty's weak points are the pyramid spikes embedded in his chest, The Chosen One makes wooden dummies, embeds similar spikes onto their chests and attempts to pluck them out with his bare hands. His hands are battered and he is exhausted, but after Ling treats his wounds and gives an inspiring speech, he finds himself rejuvenated and successfully pulls off the attack.
Meanwhile, Betty is called by the mysterious Evil Council and learns that The Chosen One is alive. The Chosen One confronts Betty at the temple. They fight evenly, until the Evil Council reveal themselves to be aliens from France, and gives Betty supernatural powers. Betty viciously beats up The Chosen One, who, in a semi-unconscious state, sees visions of Whoa and Mu-Shu Fasa giving him advice. Mu-Shu instructs him to open his mouth. As soon as he does, Tonguey flies out and attacks the mother ship, causing the entire Evil Council armada to panic and retreat, leaving Betty vulnerable. The Chosen One rips the pyramid spikes out of Betty's chest, killing him. As The Chosen One returns home with Ling, his tribulations are far from over, as presented in a trailer for a fictional sequel, Kung Pow 2: Tongue of Fury, that immediately follows the final scene.
In a post-credit scene, Master Tang asks someone to help him from an eagle pecking his leg.

Question: who is the ill and slightly deranged sifu?
Answer: Master Tang