evilbob said:
All of those are good points. I guess in my opinion having another character soaking up HP damage is less of a boon and more of a drag on resources; especially considering that even those very nice animals mentioned above will never actually hit anything at high levels. It's like having a moving, extra HP storage box with bad-to-ok AC that will constantly drain your cure spells. On one hand, it's nice because it's another thing they're hitting that's not YOU, but on the other hand, why not direct those creatures toward attacking your tank, who probably has the AC to keep many of those blows from landing? In other words: it's just not a very efficient HP soak.
At level 15, a dire bear companion has 14 HD, an a +21 attack dealing 2d4+11 damage.
With Greater Magic Fang, that's +3 (+4 at level sixteen) i.e. +24 (2d4+14). Improved natural attack would mean it's 2d6+14. With animal growth, that's then +27 (3d6+18). With Bull strength +29 (3d6+20). At this point, he'll hit every CR 15 creature in the MM except on a natural 1, except for the marut, which has AC 34.
By level 18, he'd have +2 HD (here +2 bab) and the magic fang would be 1 better, and, having 16HD, he'd just reach another str increase (to 34)
that's +33(3d6+22), buffed as above. A CR 20 Balor has AC 35, a pit fiend AC 40. He'll hit them, all right. Damage reduction would be a problem, so he won't do much damage - but that's OK.
And the only spells we've used so far are Greater Magic Fang, Animal Growth (free if you're growing summons anyhow), and Bull strength.
Then there's the advantage of flanking, always handy to have. And, you could turn into a dire bear yourself, when wild shaping, potentially sowing confusion amongst the enemy (which bear is the more dangerous?) You could stick an empowered summon natures ally VI in an 8th level slot, and have another five bears for extra confusion. Your animal growth will grow all of them at that point.
And I haven't even looked at high-level animal companion buffs. There might be quite a few quite powerful ones, especially with Companion Spellbond allowing Personal Range spells to be cast on the animal companion...