Anxiety

Psychological Stalker. Anxiety selects one target, typically preying upon those under a lot of stress. Anxiety is only visible to its target, also ignoring magical sight. It does have a physical form, despite being invisible, so other means can reveal it, but the raw form of it can only be seen by its target. When the target dies, it can immediately select a new one. It gains advantage on every attack made against its target. It always knows where its target is, having a blindsight of 10 feet originating from its target.

Ever-Present Horror. If the anxiety gets more than 300 feet from its target, it can teleport to anywhere within 100 feet of its target.

Traumatizing Claws. Whenever Anxiety makes a Strike against its selected target, the target makes a DC 5 Wisdom save. If the target succeeds, the DC increases by 5. If the target fails, add 1d6 Psychic damage for every failed save. When the target fails a save, it resets the DC at 5.

Subterfuge. All creatures have disadvantage on investigation checks for illusion spells within 120 feet of Anxiety.

Spellcasting. Anxiety is a 1st-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +3 to hit with spell attacks). The Anxiety has following Wizard spells prepared, and does not use spell slots:
Cantrips (at will): Minor Illusion
1st level (infinite slots): Silent Image

Multiattack. Anxiety makes two attacks: two Unarmed Strikes. It can only make the second attack against its selected stalking target.

Unarmed Strike. Anxiety makes an attack, swiping with its claws, dealing 2 damage(Plus whatever bonus Traumatizing Claws adds, see Special Traits.)

Its bonus actions are just bonus actions, with no additional rules and conditions.

Spellcasting.  Anxiety is a 1st-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +3 to hit with spell attacks). The Anxiety has following Wizard spells prepared, and does not use spell slots:
Cantrips (at will): Minor Illusion
1st level (infinite slots): Silent Image