Complex sentence: From his Master, Suvarṇadvipi Dharmakīrti, Atiśa learnt one meditation that became one of Tibetans fundamental meditation techniques, i.e., tongleng, a meditation that transforms negative energy into loving and healing energy.
Split into simpler sentences: From his Master, Suvarṇadvipi Dharmakīrti, Atiśa learnt one meditation that became one of Tibetans fundamental meditation techniques, i.e. Tongleng Meditation. A meditation that aims to recycle supposedly negative energy into loving and healing energy.