In regards to the entity on the alien planet dubbed "Maveth" in Agents of S.H.I.E.L.D.'s third season: Clearly the mysterious cloaked entity that brings death to those who are near it is Jude the Entropic Man. He was an A.I.M. (Advanced Idea Mechanics) scientist who was transformed by the Cosmic Cube AKA The Tesseract; A.I.M. was organized during World War II as the scientific research division of the subversive military organization HYDRA. He is essentially walking death to anyone he touches. I have a strong feeling this plot line is going to tie in/cross-over with Agent Carter in January. Look him up!