User blog comment:Kogath/Monster Hunter Generations Discussion/@comment-25033519-20160724023554/@comment-4911512-20160724025931

Do you have the cat with Big Boomerang locked with you during the hunt? I found out that the cat with it locked needs to actually be there to unlock it.

Like I think Big Barrel Bombay is unlocked from Rathian, and I have a cat with it locked. That cat in specific needs to be with me on the Rathian hunt.

Hope I was able to help, if that was the issue you were having. And sorry for my poor wording.