I wanted to put a Boggart into my 5e game, similar to a Boggart from the Harry Potter franchise. For those who don't know, it's a magical shape-shifting creature that can transform into the worst fear of whom ever looks upon it.
A point of contention I have is what type of creature should it be? Undead? Aberration? Construct? And, what Challenge Rating should the creature be? (I'm think about putting it at around 5-7). Also, if it is unbalanced in some way, how can I make it balanced? Anyway, here it is...
medium aberration, neutral evil
Armor Class 13
Hit Points 67 (9d8+27)
Speed 0 ft., fly 60 ft. (hover, only when unseen)
STR 6 (-2) DEX 16 (+3) CON 16 (+3) INT 12 (+1) WIS 14 (+2) CHA 15 (+2)
Damage Immunities Necrotic, Poison
Damage Vulnerabilities Radiant
Condition Immunities Charmed, Exhaustion, Paralyzed, Petrified, Poisoned, Prone,
Languages Can understand deep speech but doesn't speak it
Incorporeal Detection When a Boggart is not being directly observed it is considered invisible, specifically when it comes to divination based spells. It is also immune to magics that can read its mind.
Shapechange Weakness Unlike other shapeshifters, the boggart is susceptible to transmutation spells like polymorph. If the boggart is transformed against its will into something the creature does not fear it is unable to use Terrifying Apperance.
Terrifying Appearance When a creature looks at a Boggart, the Boggart must use its reaction to immediately cast True-Polymorph on itself to transform into whatever the viewers worst fear is. The viewer must make a Wisdom Saving Throw (DC 15) or be frightened by the Bogart while it remains within line of sight. A creature can remake the saving throw at the end of their turn if they are not within line of sight, or if they willingly enact the blindness condition in some manner. It will take on all game statistics of its new form but it retains its original health. If the viewers worst fear is an inanimate object the boggart will transform into an animated version of that object as if under the Animate Objects spell. If multiple creature are observing it or if the creature has multiple worst fears, the boggart will cycle through them at random after each turn. Anytime the boggart is not in the form of whatever the viewer fears most, the viewer automatically succeeds the saving throw against being frightened.
My idea is to have Polymorph be the equivalent of Riddikulus, Is this a good idea or should I create a home-brew spell specifically for that purpose?