I know the Omega Dragon is particularly infamous for not respawning except in the Grand Gallery and also being in the All Medals room, because it's the source of Matt's most important steroid.
I couldn't find a Panda outside of said Grand Gallery, which was kind of a pain when I was trying to get the last couple of relationships. There may be one to be found but I just went "lol GG" at that.
I was thinking more a view of the map, though the thing about the Panda is interesting. I could have sworn there was a respawning one in the top right corner of the Mystic Woods, but I doubt that's the case since its blocking the path to the Leafy Boots.