1. Buckler w/two handed weapon. (What happens when you do this?)
You don't get to use the buckler, and suffer a -1 penalty to hit. Why would anyone do this? You get no benefit from it.
2. Mind Blank spell and what it blocks. (True Strike? Invisibility?)
This has been Saged. It only blocks detection spells, not true strike and invisibility. It does block scrying and see invisibility, though.
3. Advancement of a paladin's mount. (As an animal or Magical Beast? Any skill points or feats?)
Advances as an animal, and doesn't get bonus skills or feats (animals never get these bonuses).
4. Monk's use of a shield. (Can you or can you not use one without losing Wis bonus to AC, etc.?)
Nope. Sad huh? You could allow this as a house rule only.
6. Haste and the 5-foot step. (Can you get a second 5-foot step with Haste?)
I recall somewhere this being Saged. Only one 5-foot step.
8. What form does the shield spell take - and how do you determine half the battlefield? (Use a line in front of the character or use half the squares around the character?)
Use half the squares (four squares).
9. What movement is affected by Expeditious Retreat? (Everything derived from based speed - walk, run, swim, etc.; movement on land only - walk, charge, run, etc.; all forms of movement - fly, etc.?)
All forms of movement. Even a beholder would fly faster.
10. Threatening an area while unarmed. (Do you or don't you?)
Nope, unless you have natural weapons, gauntlets or the Improved Unarmed Strike feat. (It wouldn't make sense; you'd draw an AoO too, unless your opponent was also unarmed.)
11. Are gauntlets part of armor? (Can monks wear them without penalty?)
Gauntlets aren't armor, they take up an item slot. A nice DM might let you make gauntlets of ogre power that also do damage as a gauntlet. You can wear them without losing most of your abilities, but you don't get special monk damage (that was Saged, and a lot of people weren't too happy about this). If you want a monk to have an enhancement bonus, there are magic items in MoF or T&B, and Sword&Fist. Or permanent magic fang (but that's not the best way).
12. How does a Barbarian's DR work? (Does a Barbarian bypass another Barbarian's DR?)
Nope. Barbarian DR works like hardness, but doesn't reduce damage from magic, psionic or supernatural attacks. Two unarmed barbarians pounding on each other would each have their unarmed damage reduced. The upside is that a +5 greatsword hitting a high-level barbarian still has its damage reduced, while a wizard with stoneskin would have al ot to fear from that weapon.
And, as a bonus, here's few items that may be clear in the rules but many folks think should be changed, perhaps:
Claws of the Vampire and how much it heals.
Bruce has said you only heal the base 1d8 damage. If you combine it with graft weapon (eg a bastard sword), you would still only do 1d8 damage. As a house rule, you could heal all of the damage, but even some PCs have complained this is an unbalanced house rule.
Harm
Semi-official errata: Will save.
