Legion can absorb other people's psyches into his mind, either intentionally or, if he is next to them when they die, unintentionally. Conversely, in several instances Legion has had personalities manifest and act separately from him (or even against him) in the physical world; in most instances Legion has ultimately reabsorbed these personalities back into himself. Presumably, both his absorption of other psyches and the physical manifestations of his own personalities are enabled by Legion's underlying ability to alter reality/time at will.