You curse one creature to the edge of the Ethereal Plane. The target begins to shift rapidly between Ethereal Plane and the plane you are currently on. Until their next turn, when the target attempts to attack a creature with a ranged, melee or spell, they have disadvantage on that attack. At the end of their turn, the target can make a Constitution Saving Throw. If they succeed the spell ends, if they fail, they can remake the save at the end of each their turns for the duration of the spell.
Creatures that attack this target do not have disadvantage, as the spell only affects the target when they attempt to make an attack on a creature other than themselves.
This spell only affects the target when they attack other creatures. If a creature affected by this spell casts a spell on themselves, it does not impose disadvantage.
Because the target shifts between the two planes so quickly, the creature can not use this blink to move through walls, solid objects or the Ethereal Plane. They can however make attacks against creatures in the Etheral Plane at disadvantage