No Monstrosities!
Motivation
Monstrosities are a poorly-organized creature type. There are magical beasts like ankhegs and owlbears, intelligent human-like creatures like harpies and minotaurs, and weird things like the shadowspawn and mimics, so they should be moved into different creature types. Also, magical beasts in a magical world would just be considered beasts, so most of the monstrosities could just be turned into beasts.
This one simple change of turning a bunch of monstrosities into beasts fixes a lot of problems regarding beasts. For one, there are no beasts above CR 8, severely limiting the options for wild shapes and polymorphs, as well as DMs wanting to throw beasts at high-level players. It also makes the Animal Handling skill useful, along with a whole slew of beast-specific spells like Dominate Beast and Animal Friendship.
Aberrations
The following monstrosities are now considered aberrations:
- Astral Dreadnought
- Banderhobb
- Kraken
- The Angry
- The Hungry
- The Lonely
- The Lost
- The Wretched
- Trapper
Beasts
The following monstrosities are now considered beasts:
- Ankheg
- Basilisk
- Bulette
- Carrion Crawler
- Catoblepas
- Cave Fisher
- Cockatrice
- Darkmantle
- Death Dog
- Displacer Beast
- Female Steeder
- Froghemoth
- Giant Strider
- Girallon
- Gorgon
- Gray Render
- Grick
- Grick Alpha
- Griffon
- Hippogriff
- Hook Horror
- Leucrotta
- Male Steeder
- Manticore
- Owlbear
- Peryton
- Phase Spider
- Piercer
- Purple Worm
- Remorhaz
- Roc
- Roper
- Rust Monster
- Umber Hulk
- Winter Wolf
- Worg
- Young Remorhaz
Celestial
The following monstrosities are now considered celestials:
- Androsphinx
- Guardian Naga
- Gynosphinx
Dragons
The following monstrosities are now considered dragons:
- Adult Kruthik
- Behir
- Chimera
- Hydra
- Kruthik Hive Lord
- Tarrasque
Fey
The following monstrosities are now considered fey:
- Centaur
Fiend
The following monstrosities are now considered fiends:
- Chitine
- Choldrith
- Drider
- Lamia
- Spirit Naga
- Yuan-ti Abomination
- Yuan-ti Anathema
- Yuan-ti Malison
- Yuan-ti Mind Whisperer
- Yuan-ti Nightmare Speaker
- Yuan-ti Pit Master
Giant
The following monstrosities are now considered giants:
- Abominable Yeti
- Yeti
Humanoid
The following monstrosities are now considered humanoids:
- Doppelganger
- Ettercap
- Harpy
- Medusa
- Merrow
- Minotaur
- Tlincalli
Ooze
The following monstrosities are now considered oozes:
- Mimic
Undead
The following monstrosities are now considered undead:
- Shadow Mastiff
- Shadow Mastiff Alpha
Conclusion
There are some repercussions to this change. For one, the Summon Shadowspawn spell would create an aberration rather than a monstrosity. The big problem is that Polymorph would be even more powerful, letting you turn yourself into creatures of even higher CR. I personally would rule that the new form has to be equal to or less than half the target's level, if they have a level rather than CR.
Also, these changes to alter some of the lore surrounding a lot of these creatures, and maybe in a way that doesn't feel right for your setting. Maybe you feel like krakens as aberrations makes them too similar to aboleths, and maybe making them into dragons or elementals feels more right. Maybe centaurs should be humanoids, maybe minotaurs should be fiends to reflect their history with the demon lord Baphomet, and maybe all yuan-ti should be humanoids like their pureblood brethren.
Now you can play out your Dungeons and Dragons: Honor Among Thieves fantasy and be a druid who turns into an owlbear.