This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Soucouyant (Trinidad and Tobago)
The soucouyant appears as a reclusive old woman by day. By night, she strips off her wrinkled skin and puts it in a mortar. In form of a fireball, she flies across the dark sky in search of a victim. The soucouyant can enter the home of her victim through any sized hole such as cracks and keyholes. Soucouyants suck humans' blood from their arms, necks, legs and other soft regions while they sleep, leaving black and blue marks on the body in the morning.
If the soucouyant draws too much blood, it is believed that the victim will either die and become a soucouyant or perish entirely, leaving her killer to assume her skin. The soucouyant practices black magic. Soucouyants trade their victims' blood for evil powers with Bazil, the demon who resides in the silk cotton tree.