Wondrous item, rare
You can use an action to hold this minuscule charm aloft and speak its command word. When you do, the charm floats in the air where it was held and loosely dangles. For the next minute, any creature within reach of the charm can pull it open or closed (as if it were a zipper), opening or closing a gateway to the Border Ethereal each time. A creature that enters the gateway is considered to be under the effects of the etherealness spell until it exits the gateway again or otherwise leaves the Ethereal Plane.
The gateway can be interacted with from both the Material Plane and Border Ethereal, and it is large enough for a Medium creature to enter or exit through. The charm falls to the ground and becomes nonmagical after 1 minute. Any creature that entered the gateway and is still within the Border Ethereal when the charm becomes nonmagical takes 3d10 force damage and is immediately and forcefully ejected from the gateway.
Alternatively, while holding the zipper, you can use an action to force a ghost within your reach to make a DC 15 Dexterity saving throw. On a failed save, you successfully place the zipper on the ghost, and it loses its Etherealness action for 1 minute. For the duration, you or another creature within reach of the ghost can use an action to force the ghost to make another DC 15 Dexterity saving throw. On a failed save, the charm is unzipped, and the ghost dissipates and is immediately destroyed. The charm loses its magic after 1 minute or if the ghost is destroyed.
As the group of warriors barreled through the planar tear, the fleeing night hag realized—with startling clarity—that ethereal travel would no longer make for a safe escape from her once-victims' vengeful blades.