Animal Companion/Special Mount Advancement

[Xenodarkelf]

Can anyone tell me (with the support of an official source) if a druid's animal companion or a paladin's mount grow in size when they gain HD?

[Telonius]

As far as I'm aware, the Druid's animal companion follows this general rule:


Animal Companion Basics
Use the base statistics for a creature of the companion’s kind, but make the following changes.

...

Bonus HD
Extra eight-sided (d8) Hit Dice, each of which gains a Constitution modifier, as normal. Remember that extra Hit Dice improve the animal companion’s base attack and base save bonuses. An animal companion’s base attack bonus is the same as that of a druid of a level equal to the animal’s HD. An animal companion has good Fortitude and Reflex saves (treat it as a character whose level equals the animal’s HD). An animal companion gains additional skill points and feats for bonus HD as normal for advancing a monster’s Hit Dice.



Also, here (http://http://www.d20srd.org/srd/improvingMonsters.htm#sizeIncreases):


Size Increases
A creature may become larger when its Hit Dice are increased (the new size is noted parenthetically in the monster’s Advancement entry).

A size increase affects any special ability the creature has that is affected by size. Increased size also affects a creature’s ability scores, AC, attack bonuses, and damage values as indicated on the tables below.

So, if your Animal Companion happens to be one of the few animals that increase in size when their HD increases (Wolf is one of the few that does), then yes, your Companion will increase in size.

(Note that things like Crocodiles are not the same monster as Giant Crocodiles - they don't automatically become giant when they gain hd).

Same thing with Paladins. You'd need one of the Improved mounts mentioned in the DMG - ponies and horses don't increase size with HD. Griffons and Hippogriffs do.

[SadisticFishing]

That is incorrect. The size does not change. I honestly can't remember how I know this for sure, but I can basically guarantee it.

[Lucyfur]

It says so in the faq. Only the things listed in the Advancement section get added, nothing else.

[Fostire]

i think that this was asked here before and that the final decision was that since they were bonus hit dice they didnt count for size increase

[Telonius]

Hm, interesting. Hadn't checked the FAQ on that - I'd have ruled the opposite, absent the source. Anyway, that's the answer. (Of course, if you want to recruit a Large wolf as an animal companion, that would be up to the DM to set your required level ... )

[Aleron]

Hm, interesting. Hadn't checked the FAQ on that - I'd have ruled the opposite, absent the source. Anyway, that's the answer. (Of course, if you want to recruit a Large wolf as an animal companion, that would be up to the DM to set your required level ... )

Most likely it would be similar to many of the advanced animal companions from the druid list, so would be druid lvl -3 for determining the companion's stats.