Looking for a rule: What can be ridden?

[Grogg of the North]

I would look at MM pg 211 where it discusses Pseudodragon companions. They're arrogant, demanding, and require that they are well fed and treated like the most important thing in their companions life. Otherwise they'll leave. I think you'd need to work very hard on convincing a pseudodragon to be a mount.

 

[Greenfield]

Kinak's answer is a good one. So is Grog's.

The DMG section on Mounts (which I can't find in my SRD) says that a suitable mount should be one size category larger than the rider.

Reading a bit further, there's a section on Intelligent mounts, saying that they will need a lot of coaxing, via Diplomacy checks, before they'll accept a rider. It even mentions the idea of a Cohort as a mount. (It essentially says "Don't do it". It also suggests that a flying mount should be no more than 4 CR below the character.

That last point may not come into play, since the Cohort will be within two levels of the PC. The rest is pure gold.

Then we come to Grog's point about Pseudodragons in particular. They want to be pampered, made to feel important. If they abused, they leave.

So, the rules say, flat out and hard, that a Tiny creature can't ride another Tiny creature. They make it hard to recruit a Mount that's over animal Intelligence (meaning Int. 2). They discourage using a cohort as a mount. And the entry for PseudoDragon says, "Try it and I'm gone".

Thank you all. This is a very effective Dispel BS for the situation.

 

[Vegepygmy]

So I'm looking for a hard rule someplace to put an end to this foolishness.

All About Mounts, Part One: http://www.wizards.com/default.asp?x=dnd/rg/20050125a

 

[Starfox]

Am I the only one that thinks the idea of a fairy riding (probably standing on the back of) a pseudodragon pretty cool?

That said, I think Kinak is right in 3.5. In Pathfinder I think they abolished the rule that a mount has to be larger than the rider - which among other things allows dwarfs to ride ponies (both are Medium). Looking for the rule now I cannot find it. (Yes, I know this is a 3.5 thread, just thought the comparison interesting.)

 

[Jackinthegreen]

Of note is there is a feat in one of the Dragonlance books (AFB right now, so can't directly reference it) that allows a mount to be the same size as its rider. If it's a "suitable mount" otherwise of course.