Necrokinesis -Death can kill anything, except for Gods/Buddhas that predate him. He once caused a man to collapse after simply brushing shoulders with him.
Nigh-Omniscience -Death has an almost absolute awareness of the universe and therefore even exceeds that of the archangels, and is only rivaled by Gods/Buddhas.
Nigh-Omnipotence -Death has almost absolute power over the night. He was even able to alter the cosmos to cause an eclipse.
Resurrection through Death -It is theorized that if you kill him all the people/beings that he killed (directly or indirectly) will come back to life but it is unknown how far this can go back (centuries, decades, eons, milleniums)
Weather Manipulation - It is heavily believed that Death is responsible for the Great Flood of Genesis 6. He was also going to wipe out Japan with a massive flood when Sirzechs found him and offered him a drink.
Due to being the oldest even saying he predates God himself he is the strongest and is said he could destroy the other three horsemen with ease.
Illusion Casting - War could create illusions and hallucinations, which drove people to violence.
Super Strength - War can exert tremendous physical force.
Telepathy - War can read the thoughts of other beings.
Possesses the "True Scythe of Death"- due to Death saying he was bored of such a toy. War, his sister took it. The scythe is on par to a longinus since it possesses the potential to destroy Gods and Satans, even being one of the main weapons to kill the horsemen. Death however states that because he has played with the scythe for so long that it doesn't affect him as much as the other horsemen.
Due to being the second oldest she is the second strongest of all her brothers which means she could destroy Famine and Pestilence with ease"
Biokinesis - Pestilence can create, manipulate, and control diseases. He can also cause instantaneous illness in another being . It is unknown if this ability could affect Gods or Buddhas.
Mind alteration- can cause "illnesses of the mind" such as bipolar, schizophrenia, depression, etc. to most being. It is unknown if this affects Gods/Buddhas.
As the youngest of all the horsemen he is the weakest.
Unnatural Exorcism - Famine could forcibly remove a soul from its body (for a short period of time without killing it).
Gluttony Augmentation - Famine could enhance the sense of hunger in other beings, causing them to seek whatever it is they crave most until it resulted in their destruction.
Insatiable Hunger - As the embodiment of hunger, he constantly craved sustenance. This gave him the ability to devour pretty much anything - even the essences of devils and human souls.
Soul Reading - Famine can determine the state of a soul. Even being able to tell if it's "Damaged" or "how it would taste"
Telepathy - Famine is able to enter a mind even the subconscious of a mind of any being (besides Gods or Buddhas that predate him).
The Four Horsemen are among the most powerful entities in existence, however they require their rings to channel their powers through their physical forms. Without their rings, they are rendered without power in their physical form, except for teleportation.
Indestructibility - While Horsemen can take damage in their human forms,they are difficult to destroy, nevertheless it is possible with powerful weapons such as Death's scythe. Also, if their ring is taken, they are rendered powerless.
Immortality - they are potentially immortal and can live forever.
Superhuman Stamina - The horsemen don't possess the capacity to tire, and furthermore, do not require food, water, sleep, or oxygen to sustain themselves. Nevertheless, Death seemed to enjoy eating "fast food" Sirzechs states.
Telekinesis - The horsemen can manipulate physical matter through power of will.
Teleportation - The horsemen can travel from place to place instantly, without occupying the space in between.
During the Great War these four wreaked havoc on the Earth and to the three factions with nobody able to stop them. After it ending and with the seven deadly sins sealed away out of boredom they put themselves to sleep waiting for the "time of peace" to end.
Sirzechs met Death when he was about to wipe out Japan but before he could Sirzechs met him and offered him a drink. After eating from a fast food resteraunt Death enjoyed it and decide not to wipe out any land so they could keep producing the delicious food.