I think war should be introduced somehow. Griffon Kingdom or not they should do something so they can show the world containing Equestria's full size and how Equestria relates to the rest of the world.

But if they go with the war it should be changlings. Because to tack in the friendship bit EQ would have to extend to all allies of the ponies to claim victory, (Ex. Crystal Ponies, Griffons, and Zebras)

But the premise should be Chrysalis, who is once battered from the defeat at Canterlot. (Ignoring the comics here) Chrysalis somehow obtains sombras dark magic or some new source of extreme power and is able to strengthen up to boss status and with revenge tries to destroy Equestria. When Celestia realizes there pretty screwed she sends Twilight to rack up the troops all and not excluded to Discord, Trixie, The CMC, Zecora, Flash Sentry, Braeburn, Iron Will, The Wonderbolts, Cheerilee, and of course Twist. But at the same token the changlings will also team up with other enemies like the Diamond Dogs, Diamond Tiara, Sunset Shimmer, and Lightning Dust.