I'm in the Enigmatic Grotto and recently, a large boulder appeared in my path. I could try to move it or choose another path. I tried to move it and continued exploring but now nothing is happening but just normal battles. Will I ever reach Casius and if not, is it because I chose the wrong path at the boulder? I'm a little confused about this...

I can't remember which option I chose, or what the outcome was, but both paths will eventually lead to Casius. It's just you may encounter something different along either paths, but the end point will be the same. You'll just have to keep fighting until you find him. =P

Thank you!