This story is a sequel to The Advent of Godzilla

Tambelon, the most majestic city aside from Canterlot and the Crystal Empire. What stood out from either of the two is the perfect quality of the tubular bells they produced. The grandest of the bells is hung high in the castle towers. Legend speaks that should the Master Bell be rung, it’s sound can bring forth great joy. The Rams and the Ponies shared the city. But one Ram didn’t want to share his city with the Ponies. Studying dark magic, the Ram was able to drive the Ponies out of Tambelon, but those that stayed and fight were placed in a gladiator arena. Princess Celestia would not tolerate his actions. A war soon broke; many of both sides did not survive. As a last measure, the Ram leader placed his life energy into the Master Bell before being banished into the Netherworld. But somehow Tambelon would return every 500 years, and the bloodshed would begin anew.

Occurs in both the Old and New Timelines a while into Season 5 (After Appaloosa's Most Wanted).