I really don't know what Grogar's plan is. but if I remember correctly from G1 he planned to send all ponies to the realm of shadows. A perfect revenge plan would be to banish the entire pony race to a realm they cannot escape from. With Equestria empty Grogar can repopulate it with monsters and other horrid creations. It would also serve as a reminder to all creature kingdoms, no one messes with Tambelon(Formally Equestria) Fear of such a fate will keep them from challenging him. Think Cozy Glow's plan but instead of magic, its ponies.
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