I love the references that MLP G4 makes to their ancestors.  
There was an episode where Gusty the Great was mentioned and how he banished Grograr, along with his army of unicorns, to the kingdom of shadows. It was amazing, without a doubt I would have liked to hear the whole story.
 
Because of that, I could not help but imagine a thousand and one ways of how the meeting could have taken place, so here you have it, a drawing in the name of the legend of Gusty.
 
Remember that Grogar feeds on fear … And she does not fear him at all! It will be an epic battle!
 
We expect more from Grogar, and a Gusty appearance if possible, in this last season!