There are two aspects to the completion stage: the completion stage with characteristics and the completion stage without characteristics. The completion stage with characteristics includes practices that involve subtle visualizations inside the body, breathing techniques, yogic exercises, harnessing the power of sexual energies, and utilizing the states of deep sleep and dreams. One famous example of a collection of these practices is the Six Dharmas of Naropa. This collection includes: tummo (inner fire meditation), the luminosity of deep sleep, practice of dreams, illusory body, transference of consciousness at death, and navigating the bardo, or the state in between death and the next life. The completion stage without characteristics includes the practices of Mahamudra and Dzogchen, wherein one meditates directly within the unfabricated nature of mind.
This is a set of amazing instructions that Garchen Rinpoche kindly gave near the Boudhanath Stupa in Nepal in August 2012, right after doing retreat in the sacred abode of Lapchi. (15 pages)
Here is a concise accessible practice that includes the different stages of training for the transference of consciousness at the time of death, according to the Drigung Kagyü lineage of instructions. This practice includes the self-visualization of Vajrayogini and subtle channels, the visualization of consciousness, the Guru visualized as Buddha Amitabha, and the longevity practice of Buddha Amitayus at the end. (5 pages)
This pithy and profound practice, revealed by Rinchen Phüntshog in his Yangzab treasure cycle, merges Padmasambahva and Mandarava Guru yoga, pranayama, a longevity practice, and an ultimate dissolution into non-conceptual reality. (4 pages)
This is a chapter on the practice of dreams taken from a longer commentary entitled the Exquisite Words of Master Naropa: A Clear Explanation on How to Practice the Instructions of the Profound Path of the Six Dharmas of Naropa by Rigdzin Chökyi Dragpa. The text that this comes from is the main guide used in the Drigung Kagyü tradition to instruct yogis and yoginis in retreat in the practice of the Six Dharmas of Naropa for the past few centuries. This chapter on the practice of dreams presents a lucid depiction of how we can recognize that we are dreaming within dreams. It also goes into detail about the ensuing practices of emanating in dreams, transforming dreams, abandoning fear, training in illusions, training in pure realms, mixing with the appearances of the daytime, and meditating on the ultimate nature of dreams. (8 pages)