The Mandate of Heaven: The Black Tortoise Begins as the Guardian Divine Beast of a Clan

[Cultivation clan + decisive killing + intelligent protagonist + exotic beast + conquest across the Myriad Worlds] Immortals as servants and emperors as slaves? Ancestor Black Tortoise, that’s ridiculous! One day, I transmigrate and am reborn as a low-level demon beast, a Black Tortoise. What should I do? I need an answer, fast! Luckily, I have the Heaven’s Mandate Clan-Guarding System. I become the Lin family’s guardian ancestor, and from then on, the world’s logic goes completely haywire! (P.S. Lin family disciples: So you’re the Immortal Emperor, huh? Then come work as a stable hand at my place!)