Though there is little known about him and his origins, eyewitnesses have reported Jack having the following abilities.
Immortality/Invulnerability- Jack is not strictly a physical entity. As such he is not affected by age, disease, physical harm or the need for air. He has withstood being shot multiple times by various firearms at point-blank range with no signs of physical damage, stayed inside a burning building and walked out with no signs of burn damage, and has wandered within the deadly radioactive wastelands of Chernobyl without any indication of being affected. He is also shown to be virtually immortal, being alive since the dawn of recorded human history and amassing an untold amount of knowledge since then.
Superhuman Abilities- Being inhuman, Jack has displayed a number of natural abilities that far exceed that of a normal human being. He is capable of single-handedly lifting a full grown man with no apparent effort and toss them over 50 feet. He is also shown to be able to move at extremely fast speeds that barely registers to the human eye.
Presence- Jack's very presence seems to have vast psychological effects on living organisms nearby. Animals senses are higher than humans and can perceive things that they cannot. As such, Jack's presence causes them to be overcome with intense fear much like pets reactions to spirits. Face to face encounters as well as physical contact with Jack is capable of inducing madness to even the strongest of wills, although there are few that have been able to resist these effects.
Teleportation- Jack is capable of teleporting to any location, no matter the distance. This is accomplished through access of a dimension known as the Plain of Sorrows, Jack's home realm. Through access of this realm, Jack is able to teleport to any location instantly. Entering and exiting this realm appears as though Jack appears and fades like a mirage. While in his home dimension, he has complete control over every aspect of it and can warp it to his will. He is also capable of teleporting to alternate realities, dimensions and plains of existence through his access of his home realm.
Spiritual/Physical Access- As both a spiritual and physical entity, Jack is able to interact with both physical and spiritual planes of existence and the inhabitants of both plains. To an extremely limited degree, Jack is able to manipulate a victim's dreams. Unlike horror film villain Freddy Kreuger, actions and events that happen during Jack's manipulation of the victim's dreams doesn't cross on into the real world. Using this access, Jack is able to detect intimate details of those he comes across such as their personal history, thoughts, and even able to detect whether or not an individual is dying, or diseased. Jack is also shown to be aware whenever someone mentions his name, instantly knowing their location and identity the moment his name is mentioned. Through his access of the spiritual and physical plains of existence, Jack has the ability to modify and warp reality to his will, although he is incapable of using this ability to harm potential victims. Jack can alter a victim's perceptions of reality, capable of showing them events of the past, and possible futures, as well as generating rain, mist, and fog.
Shapeshifting- Jack is capable of shapeshifting into a more human form in order to get closer to his human prey. The height, weight, and ethnicity can be altered depending on the location and era he is in. However, in all cases he retains characteristics such as dark colored hair, pale skin, and black eyes (hence why some call him The Black-Eyed Man).
Telepathy- Jack is capable of communicating telepathically with individuals, speaking speaking to them in their native language. It appears Jack is either incapable or chooses not to communicate through normal means, thus only converses with individuals telepathically. He is also capable of perfectly mimicking the voices of those familiar to his victims that only they can hear, sometimes using this ability on multiple people at the same time.
Plain of Sorrows Bleeding Effect- Although he doesn't use this ability often, Jack is capable of accessing both his home realm of The Plain of Sorrows and other forms of reality simultaneously that induces a "bleeding effect" in the reality accessed known as "Dimensional Bleeding". Through this bleeding effect both realities, including Jack's home realm, the accessed realities become distorted/disrupted combination of each respective reality at the site of access. The bleeding effect also causes pieces of the accessed real to be leeched off into The Plain of Sorrows, leaving behind a listless place where no plants grow or animals wander.