This is the last mission, just after defeating Ponytail. You are able to return to free roam after this, so it isn't a point of no return.
Ignore the first Jiang Shi and sprint up the stairs. At the top, you'll take it in waves - destroy a power supply to get a Peachwood Sword, defeat the possessed monk. On the third wave, two Yaoguai will appear. If you still need the Demonic Exorcism stat award, make sure to keep a grip on the sword. After defeating the last of them, you can take on Smiley Cat. Grab one of the swords lying around and focus on him exclusively, the mission ends once he's down.