How do subordinate creatures work?

Question

So the PHB and DMG don't do a good job of clearly explaining how subordinate creatures work. It seems like it should all be one subject, but instead it's spread out in a dozen different places and only discussed as a side-note, if at all. I feel almost like it either wasn't given much consideration by the developers, or was actively being avoided/suppressed as a non-standard style of play.

• There's dogs, horses, and other "mounts" for purchase in the PHB, and there are rules for how to use them as mounts, but no explanation of how they work otherwise.

• Aside from purchasing animals, there are a few other ways to acquire subordinate animals, including the beastmaster's animal companions, the urchin's pet mouse, steeds from the find steed spell, or familiars from the find a familiar spell. These each have their own rules, but there is no explanation for how- or if- these creatures operate in the same way as some animal you bought in addition to those rules. The implication is that they are each a separate system entirely, despite being able to coexist, and possibly overlap the same monster entry in some cases.

• The DMG lists the food and water needs of creatures by size. I can't find a chart incorporating care expenses into life expenses. The purpose seems to be intended for surviving in the wilderness, but the needs of subordinate creatures are not considered by the rules at all otherwise, nor is it stated whether creatures born from find steed or find familiar need to eat.

• The PHB also lists the prices for hirelings, and the DMG lists uses for hiring them to maintain various types of property. There is absolutely no discussion about them outside of those two lists- not even an explanation of the term "hireling", which I'm assuming has the same meaning as back in basic D&D where they were a core part of the game.

• Nothing in the book states whether these things are NPCs, PCs, or something else entirely, and no advice is given on how they should be played.

Am I missing something that would explain the apparent inconsistencies, or act as a sort of root-rule that is being modified by all of these separate sections?

This question is similar, but is purely from a player's perspective and for roleplaying purposes only: Are there any documented rules about owning vanity pets in D&D?

Answer 1

All creatures are either PCs or monsters/NPCs (the terms are interchangeable). PCs are under the control of a player, monsters/NPCs are under the control of the DM. This is implicit in "What is a Monster?" on p.4 of the Monster Manual.

Any pets etc. of the PCs are monsters/NPCs and are under the control of the DM. They behave the way that the DM decides they behave.

If a player decides to use one as a mount then there are rules for this.

If there are specific rules (e.g. Ranger's companion, Paladin's mount, Spellcaster's familiar) that allow a PC to control the creature then use those. As an aside, a familiar is a "spirit" not a "beast".

Outside of these the creature will do what it wants. Of course, the PC can ask it to do certain things which depending on the circumstances the DM may decide it will or won't do. For example, there is clear real world precedent for a dog to follow all sorts of verbal commands depending on its level of training and bonding with its handler. However, for a cat, not so much. Similarly, the PC's request to an NPC to "Please pass the salt" may be followed or not at the whim of the NPC (aka DM).

As for food and water, where it is appropriate in the story for the PC to worry about those things then they should worry about it for their companions too. However, in most games, detailed logistics fall into the "no fun at all" basket and it is simply accepted that everyone gets enough to eat and drink. Obviously, if the story involves moving a herd of elephants through the desert then you may need to pay attention to this.

"Hirelings" is not defined because it takes its common English definition, "a person employed to do menial work." A PC can ask them to do anything they want and, if the PC is their employer, they will probably comply. Unless it involves significant risk, of course, or they hate the PC's guts.