Mystic Knights: Battle Thunder is a fanfictional series that could've been the second season of Mystic Knights of Tir Na Nog before it was cancelled.
Queen Maeve returns to Kells along with her new monster army. The Mystic Knights attempted to fight against Maeve's army but weren't able to against her new powerful monsters. The Mystic Knights gain the new Battle Thunder power; with this new power, they gain new upgrades to their armor & can summon the Four Sentinels of Temra to fight alongside them. Now, the Mystic Knights will fight to save Tir Na Nog from Maeve's army, among them, her own Mystic Knight, the Mystic Knight of Shadows.
- King Conchobar
- King Fin Varra
- Gorta - A street beggar; somewhat the comedy relief.
- Four Sentinels of Temra
- Giant Spider of Banshee Woods
- Queen Maeve
- Abhartach - Queen Maeve's new general, as well as Seanin's guardian.
- Cluricaun - A creature who is in charge of making monsters in his large jug.
- Slugs - Maeve's footsoldiers
- Trechend - A three-headed monster who fights alongside Seanin.
- Darrig - A monster who kidnaps the children of Tir Na Nog & leaving Slugs disguised as children in their place.