Others cannot get involved. The reason for this is because 

Others can cheer you on. Others can support you. But if a Powerful Bully is too powerful, it’s going to require a different strategy. 

The moment others help you, you stop being the Underdog, and the Power Dynamic changes. It is no different than taking up arms. If you are the Underdog, you must be the Underdog, and fight Powerful Bully-Playing the Victim, with Visible, Pure Truth.

Show the World The Truth.

This is your only option.