Androgynous goblin servant of the Lord of Darkness, Blix was a skilled huntsman and a singularly ruthless individual, never hesitating to physically abuse his subordinates to keep them in line. Along with Pox and Blunder, Blix was sent by the Lord of Darkness to hunt down and kill the last remaining unicorns in the world.
He succeeded in killing the stallion, cutting off his alicorn, and upon discovering that the severed horn possessed magical properties, Blix and his companions became drunk with power and even spoke of rebellion against their dark master.
The Lord of Darkness himself put a stop to that nonsense, making an example of poor Blunder and then sending Blix and Pox to capture the mare that they'd forgotten about in their revelry. They found the world's only remaining unicorn being guarded by Princess Lily and Brown Tom. Blix "killed" Brown Tom, and then he and Pox captured the mare, as well as Lily when the princess refused to get out of their way.
It is unknown what happened to Blix following his return to the Great Tree to deliver Lily and the unicorn. The original script by William Hjortsberg has both Blix and Pox appear many times afterwards, but in the basic cut of the movie they just disappear. The Director's Cut of the film on DVD, however, restores a scene where Darkness tells Blix that his reward for completing his task would be that he would become a prince in the dark lord's realm, so it can be readily assumed the greedy goblin went immediately away to establish his newfound princehood somewhere else.