The chapter builds on the work of previous scholars on the Esoteric Buddhist mantra in Sanskrit inscribed on a circa 8th-century gold foil recovered from the Ratu Boko prominence in Central Java, and identify two hitherto unnoticed attestations of it in two sources from Bali—one in a Sanskrit Buddhist hymn (the Pañcakāṇḍa), the other in a Sanskrit-Old Javanese Śaiva text (the Gaṇapatitattva). Through an analysis of related textual sources from the Indian Subcontinent and East Asia, my study casts new light on the context and function of the Ratu Boko artefact, and elaborates on the religious and socio-political scenarios opened up by it.