Klaus said:
How is that Wolf getting +15 to hit? IIRC, it's +4 BAB, +3 from Str 17 (raised from 15) and +1 from Weapon Focus (bite), for a grand total of +8.
Probably a typo on my part. Let's see.... 4 extra HD give +3 BAB over the normal wolf's, +2 Str/Dex gives +1 attack to put it at +8. Yep. My bad.
Mirivor:
Training for combat riding is DC 20. A Druid gets a +4 bonus on Handle Animal checks on his Animal Companion. Okay, Taking 10, at 1st, he needs max ranks in Handle Animal and an extra +2 from somewhere - Charisma 14, maybe - to make the DC. So the Halfling Druid-1 could have his wolf/riding dog trained for Combat Riding fairly readily. And he gets a bonus trick - which is used for, oh, overcoming the limitation that animals don't attack strange things ("Normally, an animal will attack only humanoids, monstrous humanoids, giants, or other animals. Teaching an animal to attack all creatures (including such unnatural creatures as undead and aberrations) counts as two tricks."). Having an animal do one of the tricks it's been trained in is DC 10 - if you can take 10 to make DC 20, you'll make that on a roll of 1. For a Druid, it's a free action to handle his animal companion, so, when the Druid's turn rolls around, he's got a medium fighter on his side, that basically always obeys, and can do all the basic fighter-1 things, and has 13 HP, AC 16, and Bite +3 for 1d6+3, plus trip. And the Druid gets a move of 40 out of it (combat riding, after all). With a dex of 10, the Druid can stay in his saddle and guide with knees on a roll of 1 (4 ranks in Ride), and fight with his mount on a roll of 6 (exactly 75% of the time). Druid can improve the Dog's AC by 3 points by spending 50 GP on Studded Leather Barding. Pricy, at 1st. More likely to go with Leather barding for +2 at 20 gp, for an AC of 18 or 19 for 20 or 50 gp from the druid, respectively. Saves +5/+5/+1
The DMG NPC Fighter-1 has AC 18, 12 HP, bastard sword +5 for 1d10+2, saves +4/+1/+1. The Druid's Riding Dog in leather barding is effectively an NPC Fighter-1 slightly specialized for tripping. And the NPC fighter spent 200 gp on splint mail, 20 gp on a heavy steel shield, and 335 gp on a masterwork bastard sword (total 555 gp, ignoring the bow and arrows). The Druid spent 20-50 gp.
Skip ahead a bit to 4th.
NPC Fighter-4 has AC 21, bastard sword +9 for 1d10+5, 34 HP, saves +6/+2/+2.
Druid now has 7 ranks in Handle Animal; with his animal companion bonus, he gets a +11, + charisma mod to Handle Animal. With a Charisma of 8, he makes the DC 20 Combat Riding training by taking 10 (same bonus trick as before). He picks up, oh, a Dire Bat, which normally has AC 20, 30 HP, Bite +5 for 1d8+4, saves +7/+10/+6. Now suppose we let natural bond work with level-adjusted animal companions. The Dire Bat picks up 4th level Druid Animal Companion Bonuses. +2 HD, +2 Natural Armor, +1 Str/Dex, Evasion. Now the Dire Bat has Bite +7 for 1d8+6, AC 22, 45 HP, saves +8/+11/+7. The Fighter averages a little more damage, and slightly better to-hit, but the Dire Bat has better AC, more HP, better saves, and Evasion. Oh, and flies. And has 40 foot blindsense. With a Charisma of 8, the Druid can get the Bat to do any of it's tricks as a free action on a roll of 1. And the Dire Bat isn't a combat optimized animal companion. Spend 40 gp to give the Dire Bat leather barding, and it's got AC 24. Oh, and that still without any buff spells like Magic Fang, Bull's Strength, Bear's Endurance, Cat's Grace, or Barkskin that the Druid-4 can share.
My suggestion? Don't let natural bond mitigate the adjustment for higher-level animal companions.... unless you're short a tank in the party.