What if in G5, The real Grogar comes to search for his bell?
Like at the very end of the S1 finale, Grogar appears.
“Greetings, puny equines. I…am Grogar. And I’ve come for my bell”.
Do not think we will see Grogar right away, it is possible that he will be saved until the final on G5 - maybe S3 or in a separate movie after the TV series.
If he had been able to break through the barrier after several thousand years, and then come in contact with the magic he had left behind in Everfree, but could not expand the scratch - he needs to become much magically stronger. He needs fear. He will create a spell that will “cut out” all active magic, without jeopardizing the magical world, with gradual memory erasure and “planting” of obsessions on all who are affected. But to use the spell he must have enormous magical power, and this he does not send through the barrier. So he will destroy the magic of Everfree, transform the energy into the spell in the shelter of the explosion that will take out his most dangerous opponents. Then he could sit for decades after decades, receiving fear magic perhaps from all over the world to become stronger, and thus be able to break through the barrier and take Equus.
In the end, he will be strong enough, and can break through to Equus with his city Tambledon which will house an army of warriors and monsters. Even without the bell, he will become very powerful, as he can assimilate and process fear magic without using the bell which is really his tool as these wands in the Harry Potter Universe. With the bell, he will use magic more effectively, even if it is empty - and most importantly; he can assimilate all magic with this. True hopelessness and despair will occur if Grogar comes to Equus.
As several had speculated, Grogar is possibly the best candidate as the final opponent of Sunny at the end of the G5.