1) DM - Decided, correct.

2) Arena - I can see debating the subtext of the arena.

3) Rules - Core RAW. - Now, you use RAW where it suits you to get MW tools of any skill, and yet bar some blatant RAW such as 9th level scrolls of any type or spell. The rules of my contest will be simple. RAW. If there are to be any deviations, there must be a detailed, well-explained reason as to WHY the banning of that particular aspect of RAW should be disallowed. Nothing concerning common sense or intuitive/counterintuitive will be accepted. The only valid reason for barring an item, rule, skill, or ability, that I can see, is that that item distorts the competition to the point of making it difficult or impossible to garner any meaningful information from the challenge.

Things that I believe will: items such as Candles of invocation, which grant incredibly powerful, repeatable abilities, with no requirement of skill or ability. A level 1 character can use one of these just as effectively as a level 10, and, with very little work, can overpower characters 10-15 levels higher than him, with ease, and nothing else. Such an item overshadows other abilities, and makes it hard to accurately assess power levels, because it overwhelms them.

Things I believe won't: scrolls of 9th level magic. They're no more powerful than a 1 shot item should be, given the cost, skill or ability restrictions for use, and effect generated. Either you must have a large amount of magical training in a class (which shows class features) or a sizeable skill allocation (which shows class skills, feat use, item selection, and the like). Both require a significant investment to gain the bonus, thus, it shows that the ability does not provide undue power to twist the test.

Also: Skill boosts for any item. It's a rather minor bonus for a rather minor cost. While it is up to each DM to allow or disallow these on a case by case basis, common sense varies greatly by the individual. Thus, the only fair way to deal with it is all skills, or none. As the bonus is minor, and there's no real reason to disallow, all MW tools will be allowed.

Also, another:

4) Starting conditions - Buff time, and the like.

Any match I give will have the definition of "buff spell" being: A spell, nonoffensive in nature, that either improves the party benefitting from the spell offensive abilities (such as improving strength, agility, or the like), defensive abilities (such as by raising dexterity, creating force shields, blocking LOS, or blocking LOE), mobility (either by effects such as Fly or haste, or by protecting those abilities, such as Freedom of movement), or detection abilities (such as true seeing, see invisibility, or various divinations, when used to gather information).

Thus, a buff spell can be one like Heroism, to boost skills, saves, and attacks, a spell like [i]Shield[/s], or Wall of Stone, or Fog Cloud (to raise AC, block LOE/LOS, and block LOS), Haste (for extra movement, AC, and attacks), or True Seeing.

The only caveats I have to buffs are that they can take effect no closer than 20 feet from an opponent. No dropping walls of stone around your opponent. Further, no effects which would force your opponent to make a save, or change his vulnerabilities in any way, in and of itself. (A spell that gives you a bonus to penetrating SR is fine. A spell that lowers your opponent's SR is not.) This does include [i]Time Stop[i] as being a spell which is not considered buff.