Calculating Adjustments for Animal Companions/Special Mounts; Need help!

[Braxis]

Okay, so I'm sitting here on the d20srd and I'm trying to find the pattern for using stronger animals in relation to the druids' levels and thus far I am stumped. At first I thought it was based on the animals HD in relation to the druids' class level, but I can see that they have varying numbers of hit dice even within the same tiers. For example, if you want to obtain a bison as your animal companion, you wait until 4th level and then he advances according to the table, but your effective druid level is a -3. How do they figure the -3? I'm really wanting to know what is the mathematical formula here and what variables are involved and how are they calculated?

First I thought it was based on druids level vs. animal HD, but that doesn't seem to be the case. Then I thought it was based on CR vs druid level, but that doesn't seem to fit either.

Surely one of you has figured out the formula and how it works. Help? Please?

Also it would be great if someone has the same formula for calculating Paladin Special mounts.

 

[Stormonu]

Generally, I've seen that summoned monsters and animal companions are about 4-6 CR's below the character they are attached to (it's definitely CR based). It's primarily to prevent the creature from dominating ove the character themselves.

 

[Braxis]

Well, since we've established that it's definitely CR based I am starting to notice something of a pattern here. It seems like the CR available to a given druid (after factoring the level modifiers) is roughly equal to half the druids' class level. In some cases, that half the class level seems to be rounded up, in others it seems to be rounded down. For example, at 7th level as a druid, you could take a 5 HD CR 3 Dire Ape, or you could take a 6 HD CR 4 Brown bear, and they would both advance as if your druid level were 6 levels lower than it actually is. I get all that. What I don't get is why these two animals are in the same tier? What made them decide to round up for the bear and round down for the ape, assuming that is anything even close to the original formula for calculating this stuff.

I just wish I knew what Wizards of the Coast was using to determine which way it should be rounded. Are they taking into account the animals' special abilities/size or other modifiers that adjust CR? I am starting to get a rough idea of how this works I just wish I had a more precise formula.

 

[Ahnehnois]

I don't think there is a formula. I think it's a de novo list of rankings.

Just as they decided that hit dice (how good it is at being what it is), CR (how dangerous it is to default PCs), and LA (how good of a PC it is) are all distinct factors in a monster, the monster's adjustment for serving as an animal companion reflects a slightly different consideration: how useful it is to the druid.

If you're trying to add more animals, I think the best you can do is look at the existing list and try to guess where your new animal fits in.

 

[Jackinthegreen]

There might be some guidelines for the animals, but don't expect a true formula for them especially across multiple books. The reason for not going with it across multiple books was they were conservative at first with CR and such, but as the game grew they felt players could handle stronger things at the same CR.

 

[Braxis]

All right guys. Thanks for the feedback. And really, the main reason why I wanted to figure out the formula (if there was one, which evidently there isn't; it's just arbitrary) is because I have seen a lot of books with feats for non-animal animal companions. Dragon Companion, vermin companion, aberration companion, etc. and I was wondering what guidelines to use on what I should allow as a DM for a given druid player to have. So far it looks like the best guideline I'm gonna get is Available CR = One half druid level. Presumably it's the same for special mounts.