Sacred Terror is similar to a normal Night Terror. However, as a member of the Fire Terror subspecies, he is red in color and has eyes that glow with red bioluminescence.
Sacred Terror and the other Fire Terrors first appear when Hiccup, Fishlegs Ingerman, and Mala enter the caves in the volcano on Caldera Cay in an attempt to put the Great Protector's egg in the volcano's lava before it becomes unable to hatch. Sacred Terror and his flock dive bomb the three humans, attempting to steal the Eruptodon egg. While they are able to keep the egg away from them, Hiccup discovers a cave painting that depicts the Fire Terror flock taking the Eruptodon egg and placing it on a dais. Hiccup realizes that the Fire Terrors weren't trying to eat the egg, but were actually trying to help it hatch. Hiccup thus offers the egg to Sacred Terror and the other Fire Terrors, shocking Mala. However, Hiccup explained the Fire Terror's motives and calmed Mala's fears about them. Sacred Terror and the Fire Terrors then placed the Eruptodon egg on the dais and flew off as the lava encompassed the egg, finally permitting it to hatch.