In the jungles, snakes are often considered some of the most terrifying things one can come across. One of two things can happen. One, you're constricted and strangled to death, and devoured to never be seen again, or the other, you're not strangled to death, and you're swallowed alive, whole, and kicking by a beast biologically designed to contain you.
Enter Shylyioxth. A 50 foot long anaconda worshipped by local tribes, whose digestive track is quite warm to represent the warm winds of the ocean, well-fed to ensure the safety of the village, and to avoid just devouring the village in its entirety. This serpent is of indeterminate age, and has been preserved for ages from tribal rituals to extend his lifespan. In truth, he started out as a pet for one of the chiefs of the tribes. He was the tribe's main method of execution to those who would betray their kin, and thus grew to be quite the large size because of it. Originally called Scxyllotloth, which roughly translates to Divine retribution, he already earned praise from the villagers for ridding them of the scum of their society.
Eventually though, even as rituals were able to prolong the serpent's life, the village chief was not so lucky. In a time of hardship, the shamans only had enough supplies to complete one of the continuum rituals, which both the Chief and his serpent were both receiving at the time. The problem is, once you had not received the ritual on time even a single time, it would no longer work going forward. Thus, the chief sacrificed his continuum for his pet. His life after this was fairly limited. As the ritual needed to be done every ten years or so, the chief only had one more cycle of 10 years to live, before his body would falter, and his spirit would move on.
On his final day of life, the chief approached his serpent. He knew that come tomorrow, he would pass in his sleep. But instead, he wanted to give himself to the loyal pet, who had stayed by his side for so long, who had been to him such a loyal friend. The serpent was hesitant to accept his friend as a meal, but given the circumstances, they both knew he would rather go in no other way. It was at this point that the serpent was switched to chief, and instead of being used as a method of execution (although he still does that regularly) Now the tribe thinks of him as the gates to the afterlife. When they near the end of their lives, he devours them, and processes them into the other side.
Thus his name was changed to Shylyioxth, or "The Afterlife".