An Ioun stone is named after Ioun, a god of knowledge and prophecy revered on some worlds. Many types of Ioun stone exist, each type a distinct combination of shape and color.
When you use an action to toss one of these stones into the air, the stone orbits your head at a distance of 1d3 feet and confers a benefit to you. Thereafter, another creature must use an action to grasp or net the stone to separate it from you, either by making a successful attack roll against AC 24 or a successful DC 24 Dexterity (Acrobatics) check. You can use an action to seize and stow the stone, ending its effect.
A stone has AC 24, 10 hit points, and resistance to all damage. It is considered to be an object that is being worn while it orbits your head.
Absorption (Very Rare). While this pale lavender ellipsoid orbits your head, you can use your reaction to cancel a spell of 4th level or lower cast by a creature you can see and targeting only you.
Once the stone has canceled 20 levels of spells, it burns out and turns dull gray, losing its magic. If you are targeted by a spell whose level is higher than the number of spell levels the stone has left, the stone can't cancel it.
Agility (Very Rare). Your Dexterity score increases by 2, to a maximum of 20, while this deep red sphere orbits your head.
Awareness (Rare). You can't be surprised while this dark blue rhomboid orbits your head.
Fortitude (Very Rare). Your Constitution score increases by 2, to a maximum of 20, while this pink rhomboid orbits your head.
Greater Absorption (Legendary). While this marbled lavender and green ellipsoid orbits your head, you can use your reaction to cancel a spell of 8th level or lower cast by a creature you can see and targeting only you.
Once the stone has canceled 50 levels of spells, it burns out and turns dull gray, losing its magic. If you are targeted by a spell whose level is higher than the number of spell levels the stone has left, the stone can't cancel it.
Insight (Very Rare). Your Wisdom score increases by 2, to a maximum of 20, while this incandescent blue sphere orbits your head.
Intellect (Very Rare). Your Intelligence score increases by 2, to a maximum of 20, while this marbled scarlet and blue sphere orbits your head.
Leadership (Very Rare). Your Charisma score increases by 2, to a maximum of 20, while this marbled pink and green sphere orbits your head.
Mastery (Legendary). Your proficiency bonus increases by 1 while this pale green prism orbits your head.
Protection (Rare). You gain a +1 bonus to AC while this dusty rose prism orbits your head.
Regeneration (Legendary). You regain 15 hit points at the end of each hour this pearly white spindle orbits your head, provided that you have at least 1 hit point.
Reserve (Rare). This vibrant purple prism stores spells cast into it, holding them until you use them. The stone can store up to 3 levels worth of spells at a time. When found, it contains 1d4−1 levels of stored spells chosen by the GM.
Any creature can cast a spell of 1st through 3rd level into the stone by touching it as the spell is cast. The spell has no effect, other than to be stored in the stone. If the stone can't hold the spell, the spell is expended without effect. The level of the slot used to cast the spell determines how much space it uses.
While this stone orbits your head, you can cast any spell stored in it. The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as if you cast the spell. The spell cast from the stone is no longer stored in it, freeing up space.
Strength (Very Rare). Your Strength score increases by 2, to a maximum of 20, while this pale blue rhomboid orbits your head.
Sustenance (Rare). You don't need to eat or drink while this clear spindle orbits your head.
This other set of Ioun Stones come from the Extra Life Adventure: Lost Laboratory of Kwalish.
Supreme Intellect (Rare). You gain a +1 bonus to Intelligence checks while this faceted sphere orbits your head.
Historical Knowledge (Rare). You gain proficiency in the History skill, or a +1 bonus to checks with that skill if already proficient, while this polished, steely sphere orbits your head.
Natural Knowledge (Rare). You gain proficiency in the Nature skill, or a +1 bonus to checks with that skill if already proficient, while this burnished, brassy stone orbits your head.
Religious Knowledge (Rare). You gain proficiency in the Religion skill, or a +1 bonus to checks with that skill if already proficient, while this tiny golden gem orbits your head.
Language Knowledge (Rare). You are fluent in one additional language while this pulsating bit of red jeweled crystal orbits your head. The DM chooses the language bestowed by the stone.
Self-Preservation (Rare). You gain a +1 bonus to Intelligence saving throws while this silvery gem orbits your head.
Notes: Bonus: Armor Class, Bonus: Charisma Score, Bonus: Constitution Score, Bonus: Hit Points, Bonus: Intelligence Score, Bonus: Strength Score, Bonus: Wisdom Score, Bonus: Dexterity Score, Buff, Detection, Utility, Warding
So how do DMs rule on the fact that they have effectively 20 hp? That seems super shitty to have someone target it and take it out but anyone knowledgeable would likely do just that at some point since they're easy to destroy. I always just ignore that part, but it seems odd that this is one of the only magic items that specifies how easily it can be destroyed, even the legendary items.
Can you still use them in weapons to make them return especially if dropped or thrown?
If someone snatches one, do they just take it or can it be summoned back to you?
What makes no sense to me is that the Stone of Regeneration, a legendary magic item. Is outclassed by the Ring of Regeneration, which also restores your body parts on top of HP at a more consistent interval and a better overall average.
Flabbergasted.
Um... the same thing that happens to anything that gets destroyed?
I would suggest you have it hover about your head at 1 foot distance, but inside a suitably large (and opaque) helmet. That won't prevent the stone from assisting you, but it should keep the stone hidden -- though as a DM I wouldn't rule against the stone breaking your concealment, since in a way, it's part of the whole process that allows you to be so stealthy and immobile in the first place.
My question is, I have both the Ioun stone of Insight (+2 Wisdom) and the Tome of Understanding (+2 to Wisdom, plus a permanent +2 increase to your max Wisdom score). Does that allow for a 22 Wisdom, from 18 (unaided) to 20 with the Ioun stone, then from 20 to 22 for the Tome? What happens if the Ioun stone is taken? Does that mean the max score drops down to 20? And if the Ioun stone is returned, does that max score go back to 22 again?
I believe RAW, the Tomes raise your max stat to 22 for any score, regardless of what that unaided score is at that time. That's the way our ref is ruling it, too.
Am I missing something, or are these really bad for their rarity?
Strength for instance gives you +2 Strength score up to 20 while it's active, which takes an action (or a handwave from your DM) and can be disabled by effects/enemies. It's a very rare item. OR you could just use a rare Belt of Hill Giant's Strength which just sets your str score to 21. As a passive effect you don't ave to worry about if active or not and unless someone undresses you, it will also stay on and is literally always superior to the stone.
Same thing with Fortitude which gives you +2 con up to 20 for being very rare. OR you could have a rare Belt of Dwarvenkind for +2 forti, poison resistance, knowledge of common dwarven runic script and a sick beard.
Like wtf Ioun stones, step up yer game, ye puny swindlin' snot nozed bastards!
completely agreed, even the stone of mastery is hilariously underwhelming compared to the other legendary items. a common luck stone adds to all your saves and abilities, the +2 caster items are only rare. unless you have no other items its not worth the attunement slot