Borc said:
1) I don't allow it, therefore it is simple, because the DMG does somewhat give rules for it but not nearly enough.
Don't allow what?
Do you ban
a) Tumbling while not walking
b) Tumbling while not using your primary form of movement
c) Tumbling while flying
d) Tumbling while flying with a maneuverability of less than perfect
?
Saying "I ban it" doesn't constitute a rule - you have to specifically list WHAT you ban.
2) It is still fun, because thats what the players make it, i am merely an arbitrator/story teller. Granted this is only my first time DMing but, i figured that you would know by now that you can only tell the story and nudge people a little bit, they have to do the work and make it fun. There are many times in the course of an adventure that a character does not get to use every single one of his abilities when it would be nice to have it. but that IS life.
Being allowed to use unique abilities of your character: Fun
Not being allowed to use unique abilities of your character: Not fun
While admittedly it is possible to run an engaging game with characters that are all identical and powerless, it's very very difficult to avoid the players getting the feeling that it doesn't matter what they do, because the DM is basically just narrating a story.
While this is certainly a choice based upon individual playing style, your selection of D&D as a system suggests that you are interested in allowing players to contribute in a meaningful way and affect the world around them. To then strip away abilities with zero contribution to the story (ie - is it essential to the plot that a flying rogue cannot tumble?) is being more than a little silly.
3)
And the fact that just because its magic doesnt mean it cannot be reasoned out. Just because its magic doesn't mean that a character should be able to outmaneuver something that has perfect flying, because that is what it comes down to. No matter how easily you want to dismiss it, that Air Elemental CANNOT do anything near as good as tumbling, and as i posted earlier there are only 3 creatures that can fly and tumble in the whole damn book, and all of those have listed ground movement too, which to me implys that they use it while on the ground. So if thats the case you might as well give anyone with tumble when they get fly cast on them perfect maneuverability because that is essentially what your doing.
An air elemental with equal ranks in tumble can maneuver better than the rogue you list.
Perfect maneuverability has a list of things it allows you to do, things that tumble CANNOT let you do.
Perfect maneuverability allows you to turn on a dime in mid air. Good maneuverability requires 1 square of movement between each turn.
Perfect maneuverability allows you to fly directly upwards at full speed. Good maneuverability requires you to move at half.
Tumble lets you avoid melee strikes. That's it. That's all it does. It doesn't affect your movement in any other way.
It certainly doesn't allow you to fly with perfect maneuverability.
Finally - I'd certainly allow tumbling while swimming. It's just maneuvering around after all.
As for burrowing - I'm hard pressed to imagine a situation where you NEED to tumble when burrowing, but I'd allow it. After all - most of the burrowing speeds are listed as 20 feet or more in 6 seconds, so these things are practically swimming through the earth anyway.