Majestic mastodon, Leviathan-inspired, underwater creature, ancient beast, massive body, long hair-like tendrils, glowing blue bioluminescent markings, piercing golden eyes, sharp tusks, majestic posture, swimming in the dark depths, eerie ambient lighting, misty seawater atmosphere, coral reef background, school of small fish surrounding, oceanic plants waving, cinematic composition, 3/4 view, dramatic lighting, HDR.