Kuṇḍalinī plays a key explanatory role in the technique of haṭha yoga in Sanskrit textual sources from the first half of the second millennium. This role increases through the corpus. Unnamed in the 11th century Amṛtasiddi, 'she' is the foundation of all yoga teachings by the 15th century Haṭhapradīpikā. In fact, she is described as the key (kuñcikā) of force in the Vivekamārtaṇḍa and Haṭhapradīpikā. Yet despite her pivotal role her description across the sources is heterogenous. This presentation traces the characterisation of kuṇḍalinī not only as snake but also as fire and fluids. She is awoken by being burnt with fire and experienced as fire or lightening flashing forth. She also produces and consumes elixirs in the body. The primordial dyad of fire and water may help elucidate the enigmatic accounts of kuṇḍalinī in premodern yoga sources.