The feats in the animal companion table are the feats gained for HD, they are not additional feats. Same as it's skills, BAB and saving throws. They are all laid out to make it easy to see what is gained at each level.
Except that... an Animal companion gets another feat at it's masters second class level, which only gives 1 HD. That doesn't math up, unless they're assuming that everything has a default 1 HD? I mean it could, but don't animals also only get a feat every 3rd HD now that I'm thinking a little harder on it?
Right, at lv2 the animal gains a HD putting them at 3 HD and thus they get a feat. This is also why with their first feat they can't take anything that requires 1 bab, because when they gained that feat at 1 HD they didn't have any bab.
Take another look at the table. An animal companion starts at 2 HD with 1 feat (the one gained with the 1st HD). This is why it has a BAB of +1 and +3 to it's good saves.
When your druid reaches 2nd level the animal companion gets it's 3rd HD and the feat that goes with it.
They get the 3rd feat when the druid gets to 5th level and the animal companion also gains its 5th HD.
They get the 4th feat when the druid gains it's 8th level, but the animal is only gaining it's 7th HD.
5th when the druid is 10th and AC gains it's 9th HD.
6th at 13th level druid & ACs 11th HD...
They have a BAB of +1 at the first relevant level of their master's class. along with a +3 to Fort and Reflex, and a +0 to will. They also gain an additional feat every second HD after level 2, not every third.
everything gets a feat at every odd HD. Your animal companion got it's first feat at 1 HD which is why in the animal companion section it says, "Note that animal companions cannot select a feat with a requirement of base attack bonus +1 until they gain their second feat at 3 Hit Dice." Because at HD 1 they didn't have 1 bab.
Then at lv2 the animal gets an HD increase and reaches 3 HD which is an odd number and thus they get a feat. You'll see as they continue to level that everytime they get an odd amount of HD they'll also be gaining a feat.
No.
You don't add the hd on the animal companion table to the monster stat block for the animal, the HD on the companion table IS the HD of the companion at that level.
The starting hit dice of an animal that could be an animal companion are irrelevant. An animal companion has the number of hit dice listed on the animal companion table for its master effective druid level -- no more and no less. And according to that table, the animal companion receives a feat at every odd hit die.
Note that all of the above is different from D&D 3.5, in case you are trying to drag in experience from that game.
You're asking a question and the answer is "no." It doesn't go much further than that. And would be abundantly cleared by reading any single companion write up in a path or module as the company doesn't do what you're implying.
That's about it.
OK, THIS is actually a valid point. Thank you Cavall.
Allow me to point out to everyone arguing HD, HD, HD, that this is part of my point. There isn't a single creature on the animal companion list that doesn't start with at least one HD. That means that the minimum level-one animal companion, once you add the two HD you get for it, is three HD. Not two. You get your second feat from Animal companion at no less than four HD, some as high as 8 (I think brown bears start with 5). So, your arguments are made moot by the actual facts.
Cavall is the only one to bring up a valid point, since he's actually citing Piazo guides and modules on the topic.
See, thats where you are going wrong. You shouldn't be using the bestiary entry as a start point. You get what is in the table in the CRB and nothing else.