The back of the 5th Edition Monster Manual, tucked away in Appendix A, there is an entry for the lowly frog. Not a magical frog, mind you, just ordinary pond frogs. It states the following things:
Frogs are amphibious.
Frogs can jump up to 10 feet.
Frogs have no attacks.
Frog stats can also be used for toads.
The poor seahorse is even worse off, as we are so helpfully informed by Wizards of the Coast of the singular defining fact:
Seahorses can breathe underwater.
It is probably obvious at this point that I have issues with the Monster Manual, and sizable Opinions on the matter, which can be summarized as “the 5e Monster Manual is a mostly-useless pile of hot garbage.”
I like hyperbole as a rhetorical device. It’s the best!
The actual point I’m going to be making in this rant / essay is that I find that the Monster Manual contains great amounts of useless information, spawned by two particular design choices.
1) Encounters are viewed through the lens of combat, even when it makes little sense.
2) Excessive categorical granularity.
The first point is fair enough for its first half. This is the Monster Manual, after all, for a game focused around killing said monsters and taking their valuables. Combat is going to be a major focus of a great many encounters.
However, people aren’t going to be marching into combat against frogs and seahorses. Representing these incidental creatures in the context of a combat encounter is a waste of space.
Gamebooks are designed around a function – their contents are meant to not only be read, but also to be used. Presenting incidental creatures (frogs, seahorses, etc) in the context of a combat encounter (something where they are not useful) does not serve this core functionality. Now, if the incidental creatures were presented in a way that provided a means to utilize them in-game in a non-combat context, (even if this use was a single sentence evoking potential uses) then they would be fulfilling their proper function – giving Dungeon Masters something that they would want to use in game.
As for the second design choice, my illustrative point shall be that 35 pages of the 5e monster manual are devoted to dragons. All fine and good for a game with dragons in the title, but these 35 pages contain the same four stat blocks (wyrmling, young, adult, ancient) repeated ten times over with only minor variation, plus the Shadow Dragon and Dracolich.
These dragons are functionally identical: a large, intelligent, flying reptile with a breath attack. The primary variables are the breath weapon, environment, and behavior, all of which can be economically fit onto a table. Those 35 pages could be easily cut down to five, providing a general dragon stat template for each age group, a list of variant traits that can be applied to different breeds, lore, art, and guidelines on making unique dragons. 30 pages could have been saved to add more creatures into the book, or add other useful features to supplement the creatures already present.
A third and final example of all this is the sphinx, a wonderful creature that has been thoroughly and utterly given the shaft by Wizards of the Coast by both design choices. The monster manual contains two separate stat blocks for sphinxes, split between male and female – it contains nothing devoted to helping DMs with riddles, which seems a massive oversight for a creature known for asking people riddles (even before attacking them). One of the stat blocks could easily have been sacrificed to provide a page-long table of riddles, but somewhere in editorial the idea was turned down, if it was ever brought up to begin with. The most known signature of a monster was completely ignored.
The end result of all of this, I find, is, a much poorer manual than what could have been, and what I believe should have been. I find it a poor book in a lot of ways, but it can be a valuable teaching aid. Its existence does not do anything to detract from the OSR cleanliness of one-line stats (HP / AC / Attack / Special Abilities) or impede the many, many folk out there who are making their own fantastic monsters that avoid these foibles.
Make your own manual, pack every page with things you want to use.
Frog: As a means of preserving an emergency heir, royal bastards are occasionally polymorphed into frogs and hidden away until needed. These frog princes are infamous for their flamboyant pondside mating displays, designed to attract wandering princesses.
Seahorse: Seahorses are believed by many to detect poison, grant potency if dried and eaten, stave off seasickness if worn around the neck, and determine the direction of incoming storms.
All of this is true. It cannot, however, breathe underwater. No one is sure how they survive.