Created by Death itself, the weapon has the unique property of being able to change form, allowing Death to utilize a virtually limitless number of shapes, but that is mainly due to the fact that Death takes many shapes when near a person or thing that's about to pass.
The scythe can virtually slay any being, even immortals. However, it cannot slay the wielder being Death yet it can somehow harm or even destroy Reapers whom are the servants of Death. However, when it comes to beings like the Great Old Ones or the Outer Gods, the scythe cannot immediately kill them, but instead cause harm to them on a spiritual level. This is due to the fact that these beings predate the universe itself, where the concept of Death was not present since the first destruction of a being was made.
Even so, while the scythe can do irreperable harm it can eventually slay the Old Ones given more than just a single strike. The scythe has also shown to be capable of destroying objects and materials as well, such as when the mere rod of the weapon touched the ground, the grassy plains were reduced to nothing but dust that faded completely from sight. It has even been shown to cause the death of celestial bodies like suns or planets, making them rot and eventually wither to the point of primordial dust from whence they were created.