After thinking a bit more on my general annoyance at the too-rigid mount choices of the cavalier class, something occurred to me. Why not take the general mechanic of how eidolons are built, and use it for all mounts/companions? Sure, not all characters will have aberrations with multiple limbs on snake-like bodies, etc, but why not use categories instead of specific animals, then customize as desired using some reasonably balanced mechanics?
For example, perhaps start with general categories such as cat, dog, horse, bird, lizard, et al. Each of those will have base statistics and "evolutions" that are unique to that category, and also some that are universally available.
Take a look at Hunter class in World of Warcraft. They can tame most "animals", and depending on your focus, certain exotic animals become tamable. Also, each animal falls into specific categories, such that certain base abilities are fixed, but there is still room to customize the pet such that two hunters with the same animal won't necessarily be identical. I'm suggesting following a similar model.
Sounds like a lot of work, but worthwhile nonetheless. If done well, it would definitely be a fun addition to the druid/ranger classes.
Honestly , good luck balancing this hehe.
This will either be awesome and create a new option to these classes (which i would quite like) or will be broken and create a demigod druid.
If you manage to augment the versatility of animals companion and to balance their effective power level (actually, many are a lot weaker than other) it could be awesome.
I propose you to create a pool of evolution like powers, with associated cost and level requirement, and then to make a list of available power for each animal in the list according to what it should be supposed to be.
For instance, a bear companion could have grab evolution, large evolution, reach evolution, rend, improved natural armor, etc. Actually they stop growing at medium size and can't even grab, witch makes them weaker than most animals companions.
On the other hand, a big cat companion should start without pounce, rake and grab and obtain these ability through evolution point. It could balance a little bit the animal companion list and allow a druid to have a specific animal companion without being weaker than...the t-rex druid or the tiger druid.
Honestly , good luck balancing this hehe.
This will either be awesome and create a new option to these classes (which i would quite like) or will be broken and create a demigod druid.
I think it will buff some animals while weakening others, overall. If done well, it should be comparable to the ARG, including the caveat that all builds get the green light from the DM in case of an unforeseen combo.
I had hoped someone might be able to assist with this, as my free time is sadly limited. I'll see if I can at least pull out the current summoner evolutions that would be appropriate for animals/mounts.
Lets just remove all supernatural evolution except maybe DR (silver?), gives free fly to bird and flying animals in exchange of ability penalties and limit evolution access to specific animal (no, I don't think a poisonous horse is a good idea -_-).
I could give you an hand to list available evolution for each animal companions to make it realistic and prevent abusive combo. If you list the evolutions you want to see on animal companions, it shouldn't be too long.
The main problem is to set the number of evolution per level, the animals base statistics, the ability progression and the size progression.
Actually, a lot of class feature such mount are based on size limitation and unbalanced power level. The reason why a paladin can only get a horse or camel his because a tiger is much stronger. In the same order of idea, the Beast rider cavalier loose heavy armor and his mount light armor bonus feat to increase his mount choices. If we equalize animals companion, class with limited companion choice will receive a boost, when the intent here is to balance this class feature and increase its possibilities.