Unlike special races like Dragons, Phoenixes, and a few other unique Spiritual Beasts who could transform into human-like form at will even in their early cultivation stages, Spiritual Beasts with mixed or impure bloodlines could only achieve humanoid transformation after breaking through to the Divinity Transformation realm.
But of course, rare Heavenly Treasures could help these beasts transform earlier.
As for whether they could learn to hide their unique beastly aura quickly or not, that depended on their comprehension abilities and innate talent.
....
Lucian emerged from the crater, his body gradually ascending into the air. His long white hair flowed behind him like moonlight, untainted by the swamp's murky waters.
He tilted his head, and the sound of his neck cracking echoed through the valley like a clap of thunder.
In an instant, like a fierce storm, the Netherworld Ghost Flames swallowed his robes, turning them to ash.
