One major idea I had was Grogar transforming himself into a gigantic behemoth in addition to his new army; An ancient, ultimate evil that represents everything that the Mane 6 and their friends stand against. Everyone seemed to enjoy that idea and I thought I'd take it a bit further here by having him attempt to literally eat one of the princesses to assert his dominance over the kingdom. A moment that would've been pretty intense for a show like this, but FIM is no stranger to intense moments, so I don't think it would hurt. '
I also wanted to put Spike in the spotlight a bit by having him be the hero of this moment. He may be small, but he has a lot of heart.