Basilisk

Wild

More than twice the size of wild Titanoboa exonantur, Serpens regulus is the largest and most lethal snake I've encountered. With a skull that's more draconic than serpentine, it possesses a powerful bite, made even deadlier by the potent venom dripping from its fangs. The unique shape of its skull allows Serpens to hunt in a way that other snakes cannot: by burrowing. Once underground, it simply waits for its victims to approach. Fortunately its forked tail is usually still visible, poking just aboveground.

Domesticated

Miraculously, survivors have not only managed to tame Serpens regulus, but ride it. Some can even stay seated while it lies in wait belowground, though I doubt it's a pleasant experience. While a wild Serpens can only be forced out of hiding by fire or explosives, once domesticated, it is easily trained to burrow or surface on command.