This is mostly a joke idea, as I'd never introduce it in a game. But playing as the Green Lantern came up in another thread, and I had the idea to create the Ring.
This is basically all of the top of my head, and I should mention, I've never read the comics, only watched the cartoons.
Let me know what you think or if you have a better method:
Ring of the Green Lantern (Minor Artifact)
Aura overwhelming evocation, conjuration and illusion; CL 21st
Slot Ring; Price —; Weight —
Description
The ring of the green lantern is a very potent artifact with many capabilities. Each ring can be charged by a green lantern battery and can hold a maximum of 50 charges. The Ring constantly gives the wearer the benefits of the spells shield, mage armor, and fly as long as there is 1 charge remaining in the Ring.
1 charge allows the use of a Magic Missile.
2 charges will cast a Searing Light.
5 charges will cast a transparent, moveable Resilient Sphere centered on the wearer with a 20 ft diameter. If outside factors (such as heat, or lack of air) would negatively impact those within the sphere, an additional charge per factor can be expended to exist comfortably. For example, if the wearer were to be on the plane of fire, 1 charge could be expended to become immune to the heat, and 1 could be expended to breathe normally for a total cost of 7 charges. Any round the Sphere is attacked, the wearer can, as a free action, spend another charge to heal all damage dealt to the Sphere. The sphere lasts until it is destroyed or dismissed by the wearer of the Ring, or until the Ring has run out of charges.
The wearer can expend 4 charges for a Shadow Conjuration or 7 charges for a Greater Shadow Conjuration.
All effects created by the Ring are colored green. To affect any creature or object colored yellow, the wearer of the ring must make a caster level check (with a bonus equal to their hit die plus their highest mental attribute) equal to a DC of 20 + double the spell level used from the ring.
A wearer of one of the green lantern rings can call forth one of the batteries from a demiplane where the lanterns reside normally. Using a lantern to recharge a ring takes a full minute of uninterrupted concentration, after which the ring is restored to full power.
Green Lantern Battery (Major Artifact)
Aura overwhelming evocation CL 21st
Slot —; Price —; Weight 2 lbs.
Description
These emerald lanterns seem to be made of pure energy. It's sole purpose is to recharge the ring of the green lantern, though other uses could exist. A wearer of one of the green lantern rings can call forth one of the batteries from a demiplane where the lanterns reside normally. Using a lantern to recharge a ring takes a full minute of uninterrupted concentration, after which the ring is restored to full power.
Well, as you suggest, this is perhaps not the most suitable item for a Pathfinder style RPG. I don't know how to make it a better fit for that framework, but I do have some questions about differences from the source material.
First, although the power battery does indeed provide the raw energy for the ring, all its effects are directed by the Will of the wearer, and there's nothing in the description hinting at this (i.e., Will saves to achieve more powerful effects, maybe expending fewer charges if you have a high WIS modifier, etc.) Also, I would recommend adding life bubble to the list of continual effects provided by the ring.
Second, it seems like those charges would be exhausted very quickly in a decent encounter, but on the other hand the charges never expire until used. Under normal usage a ring's charge should last 24 hours (it can be drained more quickly under very heavy use) and requires recharging at least daily even if unused all day.
Finally, recharging the ring only requires holding it in front of the battery and reciting a short oath. Ten minutes seems excessive. One minute should be more than enough.
EDIT: On further consideration I'm not sure about the mechanic you're using to model the ring's difficulty with the color yellow. As written it's advantageous to throw lower level spells at yellow targets rather than higher level spells, which feels strange. I suggest granting yellow targets SR vs. the ring effects instead.
The yellow weakness was fixed a long, long time ago.
The various "hand" spells and other force spells colored green should be added too. And I agree with griff the charges need to be more or no charges, the ring must be recharged every 24 hours, and every effect of the ring requires a will save to use it. Yellow objects, creatures, and characters wearing yellow should require either SR penetration or an obscene will save to affect.
I tried to come up with some mechanic that would allow for a depletion of resources, but still remain viable. Unlike in the Cartoons, the Ring can call the power battery anywhere he needs it, and recharge the ring. It only take 1 minute to recharge (not 10), so as long as no one interrupts him, he's good to go.
I thought about SR for the Ring, and my initial thought was SR = 10 + HD, then I thought, how would I calculate SR for objects?
... great, as I'm typing this I think up how to do it. SR = 10 + HD for creatures, or SR = 10 + Hardness for objects. Creatures or objects that already have SR use their own, or the one granted by the yellow, whichever is higher. Creatures with Spell Immunity are not immune to the effects of the ring of the green lanterns.
Anyway, we'll never have a direct reskinning of the Ring, as the real Green Lantern Ring would probably stomp anything we create in the ground. In the Cartoons, he could go nearly all day in an extended fight without recharging. It was very rare he ever had to worry about his ring running out of power.
I have a friend who is a major Green Lantern nut that I could ask to look over this for ideas, I'll probably do that tomorrow as he's undoubtedly sleeping right now.
how about, ring can cast any spell you want as a standard action, but you have to make a will save 20+spell lvl, if you fail, the spell is not cast, if you fail by 5 or more, the ring stops working for a day (that's not in the comic), if you fail by 10 or more the ring flies away and seeks someone more suited.
A natural one does not necessarily imply that it stops working or flies away, but it won't cast.
The caster level is 20, all spells are cast like if the wearer would have cast them using his will save +10 as save DC.
The ring is intelligent and automaticly counts as familiar, thus shares all the spells.
Major science fiction artefact.
I always thought it would make a better item dependent template vs. the Wizard builds I’ve seen.
Basically requires a high wisdom score (will modifier) to even wear it cause when Oliver Queen attempted to fire one arrow with it and it nearly knocked him unconscious. The higher the wisdom the bigger creation pull it gets before needing a recharge. Basic abilities before charges come into play constant mage armor, comprehend languages and flight
You don't list any stats for the sphere in regards to damaging it
Maybe the green layer of the prismatic sphere?
That doesn't have hit points. It's just negated by passwall.