It’s actually a good thing Grogar never officially appeared in MLP, it gives fans a chance to have fun with his character, and think up imaginary scenarios.
 
Here, Grogar came back thanks to the help of Bray a loyalist and Grogar personality cult leader, feeling that Equestria was better off under Grogar.
 
Here in the new empire of Greater Tambelon, slavery is legal, places have been renamed to compliment his ego(similar to Alexander the Great) The Mane 6 are leading a rebellion against him, basically it would be a whole season dedicated to ending this tyrants rule.
 
Spike was captured along with Gabby after being tricked by Bray who pretended to be their friend trapped them and brainwashed them into joining his cult.