Board Thread:Game Discussion/@comment-10782738-20130716165618/@comment-11368661-20130717063224

122.29.192.122 wrote: Does anyone know how to trigger the ?? bosses? I have a theory that maybe they are only for low ranking bosses. Or just random in general?

For me, it's been random. Problem being, it only activates during a co-op and I'm blowing them away so I get nothing out of it.