I'm running a 3.5 homebrew, with a fair number of house rules. In my game, dragons come in two categories: standard 3.5 and bestial. One of the PCs is a halfling Beast Master (from Complete Adventurer). I encouraged him to take a bestial white wyrmling as an animal companion, and allowed the dragon to grow as it gained HD to a maximum of Medium size. The time is drawing near when he will be able to ride it as a mount. Aside from the obvious, that I really should not be doing this!, I'd like some feedback on how to make this work. Bear in mind, this is all my doing. I'm not being pressured by the player. In fact, its more like the other way around. I think the notion of a dragon-riding PC is too cool not to give it a try!
He is one of a party of 4, all 10th level. Each character is multi-classes and not all optimized. I've been targeting their CRs at -1 (so 9th now) to compensate. The others have similar boons. My goal is make them each worth a +1 to effective level.
Overall, a young white dragon is only a CR 4, so I don't see this as being game threatening. However, it will grant the character certain advantages. These are the problems I already anticipate, and how I plan to handle them.
At will breath weapon When he first gets this companion, an extra 3d6 cold damage every 1d4 rounds is going to be over powered. This is easily compensated for by adding hit points to the enemies, and throwing in a few cold resistant/immune challenges.
Natural attacks A BAB of +9 and the low damage potential of a young dragon's attacks means I should not have to worry much against CR 10+ encounters. What little damage he's going to do could easily be offset by a few more hp on the enemies.
Spell-like abilities Bestial dragons don't have them.
Blindsense This has already been a problem with the dragon as an animal companion. Its very difficult for enemies to hide or sneak around the Beast Master character. I'm not sure what to do about it, except to go with it. The party is a lot less vulnerable to sniping. I just mix up my encounters well, and let them have an easier time when foes try to get the jump on them.
Mobility Here's the one I'm worried about. I capped the dragon's movement rate at 150 feet, ruled that it will be encumbered while carrying a riding, reducing its rate to 100 and maneuverability to poor. I'd still let it hover, if the dragon takes a feat (I think there is one, but I can house-rule if not). That still leaves a PC that can move 100 feet and make a full attack! Then again, I worry that reducing maneuverability to poor will be too much of a pain for him in a tight dungeon setting.
Well folks, that's my conundrum. I would appreciate some feedback and constructive criticism.