The Blood Bar is your HP Bar and your Stamina Bar at once. It was supposed to be a single bar that the player was supposed to keep an eye on and maintain in their attempts to escape the valley. As for the "Thirs for Blood" that mainly focuses on the monsters I selected for this Game Jam: The Yara Ya Ma Ya Who. They're basically frog vampires. It's a little weird unless you read the hidden notes in the game and get a better understanding of the lore.
But I'm glad you liked the game nonetheless