Imagine walking in the woods...maybe you're camping with some friends, or you're vacationing and staying in a cabin with a view...and you hear a baby crying. Do you venture out to see where the noise is coming from?
If you do, there may be a chance it's a tiyanak...in which case, I'd be surprised you're here now! Tiyanak are spirits of babies with no souls, vengefully seeking out victims in the wilderness.
Different regions have different descriptions of them. For some, it appears like a newborn baby, then transforms into its "true" form when attacking. The Tiyanak may form sharp teeth and claws to attack its victims. Some say it turns into a little old man with wrinkled skin, one leg shorter than the other, forcing it to leap or crawl towards its victim.
Tiyanak are born from the deaths of unborn children, buried in its pregnant mother, and thus are born "in the ground." A similar variant says that Tiyanak come to be from stillborns or from the death of both the mother and child during childbirth. It's believed that their spirits cannot go to the afterlife because they were never named.
Spanish colonization changed the stories of the Tiyanak. Instead, the Catholic version says that they are the souls of those who died before baptism. Another modern Catholic version also says that Tiyanak are aborted fetuses who come back to seek revenge for depriving them of life.
Similar to the Tikbalang, a traveler may protect themselves from the Tiyanak by wearing their shirts inside out.