I was selling balrog vip service。When it hp to 30%，balrog turn into invincible condition，and there is no tombstone can hit to break his invincible condition.
When the balrog is in black, a mini balrog and tomb will appear. If the tomb is not destroyed within a certain period of time the balrog will continue to be black and invincible with magical powers. It has been reported and will likely be cured in the next update What we can do now is to be the first to destroy them when they appear
