This battle is what ultimately turned the conflict between humans and trolls to a standstill, ending the War for the Surface Lands.
The exact date and year of the battle is unknown, but it happened in the middle of the Dark Ages, 900 years prior to the events of Trollhunters.
The battle took place between the Gumm-Gumm army led by Gunmar, who was trying to take control of the surface lands, and several other Trolls and Humans who opposed them, led by the Trollhunter, Deya. The battle reached its close when Deya put the Amulet of Daylight in the Killahead Bridge and banished Gunmar and all the Gumm-Gumms (except Bular) into the Darklands.
Unbeknownst to the trolls, Merlin and Morgana engaged in an epic duel for the fate of the world during the course of the battle. Merlin successfully triumphed over Morgana, using up most of his magic to banish her by confining her in a crystal prison within a Heartstone underneath what would later be called Arcadia Oaks.
After Deya banished Gunmar, she instructed the trolls to tear up the Killahead Bridge stone-by-stone and send the pieces to the farthest corners of the world.
Centuries after the battle, the Killahead Bridge was reconstructed by Bular, along with the Janus Order, in order to free Gunmar and the Gumm-Gumms from the Darklands. They managed to steal the Amulet of Daylight, but everyone later discovered that only the Trollhunter could use the amulet to open the bridge.
The Changelings kidnapped Blinky, the mentor of the new Trollhunter, Jim Lake Jr., in order to force him to open the bridge. Although this at the beginning, it turned out Jim managed to alert his allies of his whereabouts and thus unleash a battle against Bular, the changelings, and goblins.
At the height of the battle, Stricklander successfully as able to open the bridge. However, Draal manages to pull out the amulet in the last minute, resulting in the bridge being destroyed at cost of Draal's arm.
After the events that occurred in Wizards, the timeline changes and in this parallel timeline the battle is reinforced by Jim, Claire, Douxie, Steve and the lady of the lake. In addition, it is Douxie who locks up Morgana, implying that Merlin later transferred power to Douxie to fall asleep.
- Blinky Galadrigal
- Claire Nuñez (alternatively)
- Deya the Deliverer (co-leader)
- Douxie Casperan (alternatively)
- Draal the Deadly
- Dictatious Galadrigal (defected)
- Good Trolls
- Jim Lake Jr. (alternatively)
- Kanjigar the Courageous
- King Arthur (co-leader)
- Steve Palchuk (alternatively)
- AAARRRGGHH!!! (defected)
- Arcane Order
- Gunmar (leader)
- Many Gumm-Gumms
- Gunmar and his Gumm-Gumm Army are banished to the Darklands by Deya.
- Merlin confines Morgana in a crystal prison underneath a Heartstone in what would later be known as Heartstone Trollmarket, using up most of his magic to stop her from unleashing the Eternal Night.
- Dictatious fakes his death and joins the Gumm-Gumms.
- AAARRRGGHH!!! defects from the Gumm-Gumm Army and joins the good trolls.
- Nomura is banished into the Darklands.
- NotEnrique reluctantly but ultimately defects from the Janus Order and joins Team Trollhunters.
- Draal loses his right arm after he removes the amulet from the bridge, tearing the bridge into pieces once more and preventing Gunmar from escaping.
- Bular is slain by Jim, but he is later smashed to pieces by AAARRRGGHH!!! when he tries to kill Toby.
- AAARRRGGHH!!! renounces his pacifist oath so he can protect his friends.
- Blinky and AAARRRGGHH!!! gather up the pieces of the Killahead Bridge from the museum and store them into Heartstone Trollmarket.
- Stricklander flees from Arcadia.
- The Second Battle of Killahead Bridge is one of the only major events where Claire Nuñez does not participate in, due to covering for Jim in the Romeo and Juliet play and not being experience with fighting yet