The Serpent could be a colossal snake, similar to Norse mythology's Jormungandr, tied to Elbaf lore. Undoubtedly, one of the main talking points in One Piece right now is the Serpent of Hellfire ...

The World Serpent from Norse mythology was known to cause tremendous tempests by moving through the ocean depths, much like how Dragon seems capable of summoning powerful winds and rainstorms at will.