You have to bear in mind that, as it spread through the world, Buddhism was either taken up in whole or in part. In some cases it was simply added to existing beliefs, even if those were supernatural, and a local religion would become a mix of Buddhism and those beliefs. In Tibetan Buddhism, where there seems to be a strong theme of hell, gods and demons, in fact they're representative of different aspects of life, such as anger and lust, and ultimate nature, and are not meant to be taken literally as real. Some branches of Tibetan Buddhism are a mix of both Buddhism and the pre-existing shamanistic religion that was present before Buddhism arrived there, Bon Po. Bon po has a pronounced magical theme and its symbolism and ideas still filter out into other forms of belief in Tibet, including Buddhism. Basically, any supernatural facets that are found in Buddhism have usually, been added to it at a later time.MelT
Reincarnation or rebirth is a repetitive experience in one's life. Psychedelics can tell this tale, but as can meditation. The Tibetan Book of the Dead isn't necessarily about one's actual dying, but one's ego center crumbling and a new one arising after some moments in the first and second bardo.