Ancient folklore from Chile’s Mapuche people has a vampiric leviathan called Cai Cai Filu.
This vampire lives at the bottom of the ocean, while in his natural form he’s a tsunami or a tidal wave. He can shape-shift into an ox or horse. (I’ve only been able to find him represented as a snake-like god. Many ancient cultures of Pre-Columbian America had snake-like gods.)
Regular sacrifices are given to this constantly hungry Godlike vampire, to keep him from attacking the village in the form of a tidal wave.
When the Mapuche melted their traditional religion with the Christianity that was brought by missionaries, they reduced Cai Cai Filu from God status to demon. He’s now a consumer of sinners.
Cai Cai Filu’s myth goes deeper than the vampire aspect.(Some don’t speak of the vampire aspect) Cai Cai wanted all earth under his control and so he would cause the water levels to rise. Tren Tren Vilu (or Tren Tren Filu) was a good serpent, who would fight Cai Cai. Tren Tren would raise sea levels until he defeated Cai Cai and the earth was safe.