Ominous Invisibility. The lurker is permanently invisible, and no creature other than the Humanoid targeted by its Stalking trait can perceive it (through normal or magical means). If the lurker attacks or if its prey manages to perceive it through normal or magical means, this trait doesn't function as long as its prey is alive.

Stalking. Charisma Saving Throw: DC 14, one Humanoid within 30 feet of the lurker that it can see. Failure: The lurker stalks the target, stays within 30 feet of the target at all times, and can't use this ability again until it or the target dies. While being stalked this way, the target is overcome with paranoia and gains disadvantage on checks and saving throws. Success: The target becomes immune to this effect of all lurkers permanently.
When the affected target finishes a long rest, it is targeted by the following effect. Wisdom Saving Throw: DC 14. Failure: The target gains no benefit from that long rest and instead gains one level of exhaustion. Once per day, the target can make a Wisdom (Perception) check contested by the lurker's Dexterity (Stealth) check to try to perceive it. If the target can see invisible creatures, it automatically perceives the lurker.