This is the point at which you can do optional side quest things if you're interested in that kind of thing. Chapter 2 has two main secrets: the Zombie Dragon and the Arena. If you're just interested in the plot, feel free to skip ahead to the next section.
This 'superboss' can be found in a secret area of the Catacombs called Social Fox's tomb. Return to where you battled Moric, and you'll find a passage behind him which leads to this secret area. There are powerful monsters here, and secret passages that you should check your map for. The dragon awaits at the back.