From Gwendolyn Taunton’s Tantric Traditions: Gods, Rituals, & Esoteric Teachings in the Kali Yuga (2018), in page 42,
Tantric Buddhism is a syncretism of Buddhism, Tantric technique and an indigenous form of shamanism known as Bon. Within Tantric Buddhism, there are also rituals which are clearly derived from shamanic sources.
Then, further in the same place, Taunton cites the following block of text from Mirceda Eliade’s Shamanism: Archaic Techniques of Ecstasy (2004), in page 436,
We cite some Tantric meditations whose object is the practitioner’s stripping his own body of flesh and contemplating his skeleton. The yogin is asked to imagine his body as a corpse and his mind as an angry goddess, with a face and two hands holding a knife and a skull. “Think that she severeth the head from the corpse …and cutteth the corpse into bits and flingeth them inside the skull as offerings to deities.” Another exercise consists in his seeing himself as “a radiant white skeleton of enormous size, whence isueth flames, so great that they fill the voidness of the Universe.” Finally, a third meditation sets the yogin the task of contemplating himself as transformed into the raging ḍākinī, stripping the skin from his own body …These few extracts suffice to show the transformation that a shamanic schema can undergo when it is incorporated into a complex philosophical system, such as Tantrism.