Why do animal companions go from 2 HD to 16 HD?

[Knitifine]

This has always struck me as a dumb way of scaling them.
Why are they made to fall off so hard in the late game?

[Gruftzwerg]

because early game you just rely on pure race/class abilities. later you should have enough magic if you really wanna focus on your animal companion. Imho it's just a regular balance curve. Early game everything you get feels ok/strong but will fall off if you don't invest into it with your build/items late game.

[Fizban]

Because WotC thinks (or at least thought for most of 3.5) that generic animal or other monster hit dice are worth as much as actual class levels, so companion creatures must scale slower than PCs. Starting companions get away with having hit dice because they want it to be a 1st level ability that gives you a real horse or wolf, so they just ignore the starting HD. Unless you're a Ranger, in which case you must have weaker class features than the full casting Druid, or a Paladin, in which case your special magical horse must wait until 5th level instead of 1st because reasons.

Not that you should ever be using the animal companion progression anyway, since scaling up a low level companion results in garbage. There is no reason not to have the biggest baddest animal you can get aside from adventuring in small spaces or the DM enforcing availability (something no optimizer ever admits but any DM can enforce with the greatest of ease).

For bonus points, consider how animal companions worked in 3.0: they were controlled by hit die pool from a 1st level spell similar to Animate Dead, and had no scaling whatsoever. This meant that at high levels your animal companion was even worse than it is now (not that it's actually bad at all right now), since you just had more unmodified animals. This presumably is what forced them to print super legendary animals in MM2 so high level druids had something that could survive a fight without being a 40' long dinosaur, because the heroic nature of 3.x was quite at odds with horde of animal "friends" suicidally charging level appropriate foes, and heaven forbid you have a class feature that's not useful in combat. Always learn your context.

[Extra Anchovies]

Because have a second set of actions is very, very powerful. Especially when that second set of actions comes with its own hit points and space on the battlefield. They're strong enough even if they only ever use Aid Another, provide flanking, and block enemy movement; they don't also need to be significant damage sources.

They start with 2 HD because animal RHD aren't maxed at 1st so they'd usually be downed in a single hit with only 1 HD.

Of course, Paizo went ahead and handed out motherf**king dragons (http://www.d20pfsrd.com/classes/core-classes/druid/animal-companions/drake-companions), with all the chassis benefits that provides (HD, BAB, skills, saves) to the Ranger (http://www.d20pfsrd.com/classes/core-classes/ranger/archetypes/paizo---ranger-archetypes/drake-warden-ranger-archetype), Cavalier (http://www.d20pfsrd.com/classes/base-classes/cavalier/archetypes/paizo---cavalier-archetypes/drake-rider-cavalier-archetype), Paladin (http://www.d20pfsrd.com/classes/core-classes/paladin/archetypes/paizo---paladin-archetypes/silver-champion-paladin-archetype), and Druid (http://www.d20pfsrd.com/classes/core-classes/druid/archetypes/paizo---druid-archetypes/draconic-druid-druid-archetype). And of course the Ranger gets a bunch of extra restrictions put on theirs, because screw rangers, am I right? Whether the addition of Drake Companions is good or bad I don't know, nor do I know why Hunters didn't get an archetype (probably cuz Hunter is mostly just a weaker Druid so everyone keeps forgetting about it), but it could certainly shake things up.

[Fizban]

Also valid points, and more for me to put on the "lol, Pathfinder" folder. Really getting a chip on my shoulder there.

[Ninjaxenomorph]

Given how many restrictions you get, I'm not inclined to like drake companions over normal companions. It's weird though that those archetypes were written by the same guy that made the Dragonrider and Dracomancer 3rd party books.