Wondrous Item, rare
This rope is 30 feet long and weighs 3 pounds. If you hold one end of the rope and use an action to speak its command word, the other end darts forward to entangle a creature you can see within 20 feet of you. The target must succeed on a DC 15 Dexterity saving throw or become restrained.
You can release the creature by using a bonus action to speak a second command word. A target restrained by the rope can use an action to make a DC 15 Strength or Dexterity check (target’s choice). On a success, the creature is no longer restrained by the rope.
The rope has AC 20 and 20 hit points. It regains 1 hit point every 5 minutes as long as it has at least 1 hit point. If the rope drops to 0 hit points, it is destroyed.
Notes: Restrained, Control
It is only 30ft long. And the within 20ft limit outward would seem to indicate it takes some end bit of it for normal types of enemies like medium or large size to really do the tying up job, can't imagine how long it'd need to be for that!
Athletics and acrobatics are a type of strength check and dexterity check. Specifically as Strength (Athletics) check and a Dexterity (Acrobatics) check.
so if you restrain a creature with this, and then grapple them prone with your own grapple, do they have still only have a dc 15 to get out of the rope's entangle/restrain challenge? or is your grapple attempt mearly a help action on the rope's restrain attempt? (or vice versa)
The description states "You can release the creature..." implying only the wielder can release the restrained creature using the command word. It would not make sense for someone else to be able to use the command word, otherwise the restrained creature could release themselves if they were able to hear the command word.
Honestly it would be sensible to give it resistance to bludgeoning and piercing damage