After the tribe successfully repel the first attack from the outsiders, trophies were earned, attributed to the fiercest warriors. But most of them remained unclaimed as the Unmaker didn't want them. He saw the cost of his pact, and tried to reject it. But the deal was made, and if he didn't want to wear them as shields and armors like his peers, the demonic essence chose for him. The many trophies were piled up, high like a man, in a gory mountain. Then, as the light from the celebrating bonfires died, as the moon disappeared in the sky, that mountain shaked. Moved. Rose.
From the pile of guts and bones, a mindless monster emerged. Both a protector for the leader, and a souvenir of his pact. Never could he walk back.