A friend of mine and I are building a wondrous item. It was originally his brain child, but I'm helping with it. The whole concept is a wrist slot item for spellcasters that would provide a shield bonus to AC in exchange for spell energies. What I would like from you, the community, is to read each of our given descriptions, tell which sounds more balanced/effective for gameplay, and possibly give suggestions on the whole.
His idea:
"This wrist slot item, only usable by spellcasters, grants a +10 shield bonus to AC each day. When the spellcaster casts a spell while wearing this item, the shield bonus is reduced by a number equal to the spell level used per spell cast during that round (to no less than 0). Example: casting a fourth level spell reduces this AC bonus to a +6 shield bonus until your next turn. In the case of quickened spells, these multiple spell levels stack for this purpose. Example: casting a quickened 1st level spell and then another 1st level spell effectively reduces the bonus by 6 to a +4 shield bonus to AC until your next turn. This AC bonus is negated during attacks of opportunity made against you and triggered by movement and/or spellcasting. If hit by an attack of opportunity, you must make a concentration check (DC = 10 + damage dealt + spell level) or lose the shield bonus for the day."
My idea:
"This wrist slot item, only usable by spellcasters, grants a shield bonus to AC each day. This bonus is determined at the beginning of the day while the spellcaster is going about his/her daily morning routine. The spellcaster selects a level of spell he/she can cast and gives up the ability to cast those spells for the entire day in exchange for a bonus to AC equal to the spell level given up plus one. Example: should the spellcaster give up their sixth level spells for that day, they are granted a total of a +7 shield bonus to AC for that day. As a free action, this effect can be discharged in order to allow the spellcaster to use the spells of the level given up at the beginning of the day. However, this item cannot be activated again until the spellcaster has fully restored their spells per day either via sleep, meditation, prayer, etc."
Additional Thought:
I also like the idea of the item being enchantable such as the Bodywrap of Mighty Strikes. The enhancement bonus would stack with the Spell Level + 1 shield bonus granted at the start of the day.
Ideas?
Problem with item #1: The item provides (baseline) a +10 shield bonus for the entire day except for the few rounds that the character actually casts spells. Using the "AC bonus (other)" line on table for estimating magic item values, such an item should have a market price of roughly (10 x 10 x 2,500 gp) = 250,000 gp; even with the "spellcaster only" and "reduce protection when casting" restrictions (being generous and counting both as a 30% reduction), the market price would be 175,000 gp.
Problem with item #2: You're allowing a sacrifice of a single spell for an all-day protection boost (at spell-level +1, no less) that's readily stackable with normal protection at a higher level than most alternatives. While it's more limited than item #1, it's still very powerful, especially if you allow enhancement bonuses to be applied to a non-physical, temporary "shield."
Considering how much a combat-cleric with a two-handed weapon (or a magus, or an eldritch knight/arcane archer, or a dragon disciple/eldritch knight, etc.) would love either item, I would not allow either.
I would probably either go with an item that activated a shield spell on command a limited number of times per day (lasts 1 min per use, market price 360 gp per daily use) or an item that would allow the wearer to sacrifice a prepared spell or spell slot (as a standard action) to activate a shield spell (duration of 1 min per spell-level sacrificed). I'd estimate the pricing for the second item to be about 14,400 gp: use activated shield at CL 9 (the maximum duration), reduced by 20% for requiring the wearer to sacrifice a prepared spell/spell slot for each use; requirements Craft Wondrous Item, mnemonic enhancer, shield.
If they want a shield bonus that lasts all day (without Arcane Spell Failure or Armor Check Penalty), then they can just get a +X mithral buckler. See also ring of force shield.
Problem with item #2: You're allowing a sacrifice of a single spell for an all-day protection boost (at spell-level +1, no less) that's readily stackable with normal protection at a higher level than most alternatives. While it's more limited than item #1, it's still very powerful, especially if you allow enhancement bonuses to be applied to a non-physical, temporary "shield."
I agree with the rest, but it looks like idea #2 would have you sacrifice all spells of that level. Granted, if you can only cast one spell of that level, it's less of a problem.
Maybe sacrifice a spell level, get a shield bonus equal to how many spells/spell slots you sacrificed up to a maximum of the spell level? If you could cast 4 5th-level spells and you sacrificed them, you would get a +4 bonus. If you could cast 7 and sacrificed them, you would still only get a +5 bonus.
Does that sound better?