The DMG doesn't explicitly spell any of the following out about the Ioun Stone of Reserve:

  1. Can non-casters use the stone to cast a spell stored inside?

  2. If not, does the spell stored in the stone need to be on a character's spell list to cast it?

  3. Can the stone store spells that require concentration? If so, how does that work when that spell is cast from the stone?

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    \$\begingroup\$ Hi LogicalMagic, welcome to the site! I see from your Informed badge you've checked out our tour already to see how we work, thanks for doing that. When you reach 20 rep, you'll also be able to join us in Role-playing Games Chat if you'd like. Enjoy your stay here! \$\endgroup\$ Oct 13 '16 at 0:11
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    \$\begingroup\$ I've edited the "thanks" out of the end of your question. We tend to treat sign-offs and signatures like that as noise; we'd rather the question were as close to 100% question as possible and formalities like that are unnecessary here and reduce that clean 100%-clear signal. :) \$\endgroup\$ Oct 13 '16 at 0:13

This functions more or less the Ring of Spell Storing.

  1. Yes, as evidenced by DMG p177...

While this stone orbits your head, you can cast any spell stored in it.

  1. Yes, as evidenced by DMG p141...

The spell uses its normal casting time, range, and duration, and the user of the item must concentrate if the spell requires concentration.

Anyone can use the spells out of a Ring of Spell Storing or a Reserve Ioun Stone and the spells that are cast out of them are cast with all the "settings" of the original cast.

Example: Your Barbarian has a Reserve Ioun Stone and your party's Cleric casts Cure Wounds at 3rd level (as that is the limit of the stone's capacity) into it. Your Barbarian can at any time use that spell as though he had cast it barring any other restrictions such as incapacitated or raging (as you are in fact "casting" a spell), but the Cleric's DC, spell attack modifier and all other such relevant parameters are of those of your party's Cleric at the time of the cast.

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    \$\begingroup\$ Minor note, if the barbarian is raging, "While raging, a barbarian cannot use ... the Concentration skill ... nor can he cast spells" I would say that rage stops a Barbarian using the Ioun stone, which says that "you can cast any spell stored in it" and rage means you can cast a spell. Either way, he definitely can't concentrate while raging. \$\endgroup\$
    – Scott
    Oct 13 '16 at 3:45
  • \$\begingroup\$ @Scott Whereas I had thought it was a given that all other parameters would be taken into account for casting a spell, you are absolutely correct. I have added a bit of verbiage for clarity in the example. Thanks. \$\endgroup\$
    – Slagmoth
    Oct 13 '16 at 12:44

No Limitations Specified in the text.

Ioun Stone, Reserve (DMG p. 177)

Any creature can cast a spell into the stone by touching it while the spell is cast.

Once that spell is cast into the stone, it is waiting to be released by whomever has the stone. ("You" in the text of the description." No class or level limitation is noted, so no specific to overrule the general. That means that a non-spell caster, whomever has the stone, could cast a spell. (For example, the bar maid whom your Warlock favors ...)

You can cast any spell stored in it.

No class or level limitation in the text. That means that you (you=the one with the stone) can cast any spell. (When the barmaid casts the fireball, won't those ruffians be surprised!)


... is otherwise treated as if you cast the spell. (DMG p. 177)

Since all characters have Constitution, and concentration checks are based on Constitution, then if you need to make a concentration check, use your Constitution.

... you must make a Constitution saving throw to maintain your concentration. The DC equals 10, or half the damage you take. (PHB p. 203)

  • \$\begingroup\$ While I agree with your conclusion... your "any creature" quote is about casting a spell into the stone, not out of it. \$\endgroup\$
    – Adeptus
    Oct 13 '16 at 4:44
  • \$\begingroup\$ @Adeptus Oops, there was still some "any creature" so I edited those out as well. \$\endgroup\$ Oct 13 '16 at 17:44

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