Boggart

 Fear Detection: The Boggart can tell the greatest fears of anyone within 60 feet (A character who can not be scried upon is immune from this affect) 

Magic Resistance: The Boggart has advantage on saving throws against magic effects.  

Change shape:  The boggart changes into the worst fear of someone within 60 feet of him.  This fear must be a creature or something that can reasonably be changed into; for instance, being afraid of falling off cliffs wouldn't really work here.  The boggart can not take a form with a Cr over 15

The boggart has the actions of whatever form it has currently taken.  However, it's hit points do not change; all damage taken by any form affects the general HP of the bogart.

When it changes, the boggart may gain hit points equal to the hit dice of the creature it has become.  This may only happen once a turn.

Fear Drain. While the boggart is transformed into a creature's worst fear, the must make a DC 18 Wisdom save or be frightened of the boggart for one minute.

While the creature is frightened and within line of sight, the boggart may use an action to drain some of that creature's life away, dealing 3d8 psychic damage and healing for the same amount

Transformative action: The boggart can use legendary actions possessed by creatures it has changed into.  If the creature has no legendary actions, the boggart can make 1 normal attack for 1 legendary action, and 1 special attack for 2 legendary actions.  The boggart has 3 legendary actions per turn unless its forms specifies otherwise. 

Invisibility: While in it's normal form, the boggart can spend 1 legendary action turning invisible.  This action CAN NOT be taken while transformed.