Huànzhēn xiānshēng 幻真先生 (“Master Illusion-True”) is the pseudonym of a late-Táng (ninth-century) Daoist specialist on embryonic breathing (tāixī 胎息) whose real identity is unknown. He is credited by tradition with the authorship of Huànzhēn xiānshēng fúnà yuánqì jué 幻真先生服内元氣訣 (DZ 828; where 幼 in the DZ is a scribal error for 幻), a significant Táng treatise on breath-retention and the circulation of the Primordial Qi, and with the commentary Tāixī jīng zhù 胎息經註 (DZ 130, KR5a0131). His commentary equates tāixī with the developing practice of nèidān 內丹 (“inner alchemy”). The attribution of the root scripture [[KR5a0014|DZ 14 Gāoshàng yùhuáng tāixī jīng]] to him, advanced by the Sìkù quánshū zǒngmù tíyào, is uncertain. Related Kanripo texts include KR5a0828 and KR5a0014.