The ideology of Alangan people contains a set of the creation of superior god and the bilateral cosmology between good spirits and evil spirits. These cosmology ideas are expressed through local oral traditions such as myth, legend and epic. Based on the bilateral cosmology between the good and the evil, Alangans develop a set of ritual practices to use witchcraft and oracle to heal disease, avoid misfortune and disaster. Their epic Lumpiēn tells the adventure of Lumpiēn and his brothers, how they become good spirits and how some spirits begin to be in charge of healing human beings. In this way, the epic provides a reasonable explanation for local healing rituals and witchcrafts, so epic chanting becomes a necessary part of the local ritual healings, and epic is entitled practical functions in the Alangan community. Therefore, the epic together with local myth and legend, consists a complete set of local knowledge, which can thoroughly interpret the bilateral cosmology of Alangan-Mangyan people.