Okay, so here are some tentative plans for the AoW / Eldritch Runestone / UR Special for True Grind at GenCon 2015.
The AoW & UR Special effects are close to being finalized, but the Eldritch Runestone effect might result in some tweaks if I missed any key issues.
Amulet of Wonder
Elemental Attunement: A player wearing an Amulet of Wonder chooses an element (Air/Earth/Fire/Water) at the beginning of the adventure during the coaching session. The Amulet provides the following benefits related to that element:
1. The player gets +2 energy damage to melee and missile attacks. The energy type depends on the chosen element (Air = shock, Earth = sonic, Fire = fire, Water = frost).
2. Spellcasters casting a damage spell may choose to change the damage type to their chosen element. Spellcasters do +2 damage with spells of their chosen element. (Air = shock, Earth = sonic, Fire = fire, Water = frost).
This effect could convert force damage (Magic Missile, Spiritual Hammer, Spiritual Maul, Glow Orb, Chromatic Orb, Prismatic Spray, Stone Storm), acid damage (Acid Ray), or divine damage (Searing Light, Sunburst) into shock/sonic/fire/frost.
3. The player takes half damage from the appropriate energy type. (Air = shock, Earth = sonic, Fire = fire, Water = frost).
The half damage is factored in after subtracting any damage/energy reduction. This does not stack with "half damage from the same energy" so a Ring of Fire Resistance does not stack with an Amulet of Wonder: Fire. It does stack with half damage due to Improved Evasion or the three-piece Mithral set.
4. Each element will have at least one additional effect which will be revealed later on in the adventure.
Eldritch Runestone
Anything You Can Use I Can Use Better: When you turn in the Eldritch Runestone during coaching, you may designate any single token. You may use that token, ignoring normal class restrictions. It does not grant class abilities.
Alternatively, you can think of it as being able to use that single token as if you were of another class of your choice (without granting class abilities).
Note that the various character generator programs probably won't be able to handle this so you may need to make some manual adjustments to your character stats!
Since it does not grant class abilities, a non-Rogue (who cannot Sneak Attack) will not get an additional benefit from Boots of the Vale, Boots of Elvenkind, Boots of the Underdark, Hood of Elvenkind, or Lenses of Vital Insight. A non-Monk (who cannot Flurry of Blows or Stunning Fist) would not benefit from the Gloves of the Flying Fist or Ring of Stunning Fist.
A Bard, Cleric, or Wizard could use the Coronet of the Arch-Druid to transform into a Dire Bear by sacrificing two 2nd level spells. A Fighter or a Rogue would not have any spells to sacrifice so they would not be able to benefit.
Only a single specific token is affected. NOT all tokens of that specific name. This especially applies to thrown weapons or two-handed Rangers or if a token gets "destroyed" during the course of Grind.
If a Wizard chooses a Viper Strike Fang, then using it as a Rogue will not provide an extra effect since he cannot Sneak Attack. Using it as a Monk will not allow him to Flurry of Blows, but with the Viper Strike Set he will get the +5 Poison damage on a crit.
Non-monks can choose a Bracer of Quivering Palm but it takes up their Bracer slot and they don't get to use Flurry of Blows for a second slider. A non-Monk, non-Ranger could choose to use an Orb of Might as a weapon but they still only get to slide one weapon.
If a non-Bard chooses a Bard instrument it does nothing if there is no real Bard doing Bardsong. However, if there is a Bard doing Bardsong and the non-Bard spends an action to use their instrument, then the damage bonus will stack if the characters are using different instruments. Non-Bards using a Widseth's or Briano's can contribute their musical talents while attacking/casting. In theory you could have a two or three-piece band with the right instruments....
Can you think of any major abuses of this Eldritch Runestone effect? The best I can think of is having everyone using +2 Keen Slayer Bows or Io's +4 Ultra Keen Slayer Bows (everyone still needs to meet the DEX requirements). Or a Monk using heavy armor. Or everyone using Shield of the Phalanx (though the total AC is capped at +7 AC). You could also have some interesting synergy with Bardsong but that requires a variety of different instruments.
UR ? Special
PUPPIES! You gain a Blink Dog follower! The Blink Dog may attack with a puck (probably a Monk slider) and deal damage. Or it can run interference (giving a penalty to a monster's attack). The puppy has a moderate amount of HP and may die if you do not take proper care of it!
If multiple players use a UR ? Special, the party could very well end up with a pack of Blink Dogs! ::woof!::
Feedback and comments on these variable token effects would be appreciated!