Green Ghidorah was an character/recolor used by gojiratheking. It was his first character, and he is ashamed of it.
even gojira has forgotten but he was murdered by gypsy danger as he recalls at the end.
He also dropped dead bodies multiples times on planets.
Maybe he fought purple orga at some point?
Since he is an recolor, he has the generic powers of an ghidorian.
So just how TERRIBLE is this character?
awful. to the point his creator flat out stated in an now deleted blog that his joke characters have more personality and are more original. GTK flat out tried to bring him back as an mecha-king ghidorah recolor, but that never took off. There is literally no backstory to him, and he never played any major role. He has not been used since about 2015 but that was to mention how BAD it is. gojira straight up REQUESTED the character be removed from the canon due to that. YOU COULD REMOVE HIM FROM THE CANON, OR IN AN ALTERNATE TIMELINE WHERE GOJIRA NEVER THOUGHT OF THE CONCEPT, and the difference of the storyline of the RPverse would prove insufficent.