Act as a fantasy illustrator with 10 years of experience in dark, mythical creatures. Create a highly detailed digital painting of a fearsome hydra with [5 to 7] serpentine heads emerging from the murky waters of a [gloomy, mist-shrouded swamp]. Each head should have [glowing yellow eyes], razor-sharp fangs, and distinct scales with a [sickly green and black coloration]. The background should feature twisted, dead trees with hanging moss, glowing bioluminescent fungi, and a faint moonlight breaking through the thick fog. The composition should emphasize the hydra's immense size and the eerie atmosphere of its lair, with subtle ripples in the water as it moves. Use a dark, moody color palette with accents of eerie greens and blues to enhance the sinister vibe.