Hyakume

A hunched shape covered in eyes, hundreds of them, all open, all moving independently. It guards places rather than hunting through them - old temples, sealed rooms, the ends of corridors that should not be walked down. When one of its eyes settles on an intruder it detaches and travels with them, from then on, wherever they go, watching. They do not always notice for weeks.

Fix and Follow: 60 ft, save Wis Mind, fail save roll 2d8+3 psychic and one eye attaches to the target invisibly. The hyakume knows that creature's location permanently thereafter, at any distance, and cannot be misled about it. Cooldown 2 rounds. Grasp: bludgeoning, melee 5 ft, +4 to hit, 2d8+3.

All Eyes Open: it cannot be surprised, flanked, blinded or approached unseen, and illusions do not work on it at all. Put Out Fifty: a creature that destroys roughly fifty eyes - the DN judges generously for anything area-wide and unpleasant - leaves the hyakume attacking at Disadvantage for the rest of the encounter and unable to use Fix and Follow at all. Existing attached eyes go dark at the same moment. Removing an attached eye afterwards needs a healer, a priest, or somebody with steady hands.