What implications would a monstrosity as a player character entail?

Question

Travelers of the Multiverse Unearthed Arcana lists the Thri-kreen race, and its type is monstrosity. I am wondering what playing as a monstrosity would entail.

All things that come to my mind are benefits: not being a valid target for many spells like charm person or hold person etc., but for the life of me I cannot see any mechanical drawbacks, as many class features list 'Creatures' and 'Allies' so I see this as an overall buff.

I am wondering if I should let one of my players play as one. What are the advantages that I did not see, or what are disadvantages (if any exist) of playing as a monstrosity type PC?

Answer 1

There are no real mechanical drawbacks to the Monstrosity creature type.

You are correct that there are practically no effects in D&D5e that effect a Monstrosity differently than it would a Humanoid, unlike Undead or Constructs which can often not be targeted by healing spells. On the other hand, there are various negative effects that can target only Humanoids but not Monstrosities. Mechanically there are thus no real drawbacks to playing as a Monstrosity.

Whether or not there are social consequences within your world is up to you, although I would avoid them. They are generally not fun and only become more tedious and annoying over time. Although the Monstrosity creature type is beneficial, it is a rather situational buff and should not warrant any made-up drawbacks.

The Thri-Kreen race overall is on the strong side, but mostly because of their incredible telepathic communication. A base AC of 13 + Dex when not wearing armor is also very helpful for certain classes (sorcerer and wizard come to mind), being able to stay conscious during long rests is always of use, and their secondary arms allow for more flexibility when it comes to wearing a shield and still being able to carry more than one weapon for two-weapon fighting. So the race has a lot going for it, but nothing that I would consider gamebreaking (least of all the Monstrosity creature type).

Answer 2

Disadvantages of playing a monstrosity depend on world-building and social acceptance

Monstrosities as a creature type are described in the Monster Manual (page 7):

Monstrosities are monsters in the strictest sense - frightening creatures that are not ordinary, not truly natural, and almost never benign. Some are the results of magical experimentation gone awry (such as owl bears), and others are the product-of terrible curses (including minotaurs and yuan-ti). (...)

A typical civilized society would not be expected to allow monstrosities, that is monsters in the strictest sense, in their midst. Such creatures would be persecuted, and authorities would try to arrest and eliminate them, as they would be seen as a threat to the safety and well-being of the population. This would make the character near unplayable in social adventures, unless they had a good way to hide their true nature. It also would make it difficult to obtain any kind of healing and support from temples or other organizations, and to find lodging or buy equipment.

None of these disadvantages are mechanical in nature, but they still are very real, and can make it un-fun to play such a character, even if the character race mechanically is powerful.

In older editions, drow were an unquestioningly loathsome, evil race feared by all good folk, but had powerful racial abilities like innate spell-casting. They experienced similar issues as player characters when playing drow (especially dual-wielding rangers) became popular due to the Drizz't do Urden novels.

Social disadvantages depend on the DM's interpretation how people will react to such a character, and on world-building. For example, Thri-Kreen originate in the Dark Sun setting where they were not uncommon, and in second edition were a playable character race in the Dark Sun setting, maybe somewhat distrusted, but not automatically persecuted.

Back in 1e, the DMG advised about The Monster as a Player Character (p. 21 DMG 1e):

The considered opinion of this writer is that such characters are not beneficial to the game and should be excluded. Note that exclusion is best handled by restriction and not by refusal. Enumeration of the limits and drawbacks which are attendant upon the monster character will always be sufficient to steer the intelligent player away from the monster approach, for in most cases it was only thought of as a likely manner of game domination.

In general, D&D has become much more inclusive and embracing of diversity, with things like Drow and even demonic-origin Tieflings a common character option even in the core rules. A DM following this trend may opt to disregard many of these disadvantages, and rule that there are so many weird creatures out and about, common folk in his world will not bat an eyelash at seeing a Thri-Kreen walk down the street or order ale at the local pub.

If the DM does not enforce social disadvantages for playing a monstrosity, then indeed, the mechanical bonuses may be pure upside.