A seemingly-glass Orb, about the size of a cantaloupe, cloudy within, swirling with the color of Dragon it contains.
The Dragon Orbs are attuned to the element of the dragon whose color they share. It's less of just a 'soul in a box' and more like the dragon soul is in the Orb, which itself supplies a direct link to the Elemental Chaos, which the soul uses to have some power (like Winter's Kiss shooting ice, and Punundrum firing off lightning)
By holding them, and tapping into them (ie, holding onto them and contacting them), you develop a certain link as well, meaning they can share their knowledge or power if they so choose, but it's an easily cut bond, in that you're basically just holding hands with the Orb, but can let go at any time.
They're very special.
So, the Orbs are like special...conduits of the dragons' power, not entirely of this plane, but connected to their race on a very deep level, (their language is the source of all magic, they are beyond just 'magical creatures').
Orbs are connected to the dragons, and when a Dragon's soul enters an Orb, that Orb forges a Bond to that particular soul until enough power is in the vicinity to release the soul and let it form a new body, then the link is broken but the connection to that element remains. In this way, the Dragons have their own emergency stasis pods in case their bodies are destroyed, and keeping their power alive.
That's how it should work. But dragons have a lot of power, and the conduit to the Elemental Chaos has even more, and if an evil mage can ward off it's defenses, it becomes a very big power source. That's not the natural order of things though, and siphoning the power from the dragon's soul destroys it completely.
If an Orb is siphoned enough, you fray the link to the Elemental Chaos enough to undo it all-together. But, now it's a massive vacuum, a vessel meant to suck in massive amounts of power with nothing to feed it. This, is a Void Orb.
Bant has first-hand experience with a Void Orb, he tapped into it similar to how Thyella tapped into Punundrum or Winter's Kiss and Gauthak tapped into Scorching Heat, and so formed a link. A link to a vortex that just did what it was supposed to do, draw in power. But Bant is no dragon, nevermind a whole plane of existence, so his soul was fractured and the Void Orb remained a Void, barely filled at all by the attempt.
But, when Thyella connected a Void Orb with Punundrum's soul, it forged the Bond as it should, and between that and the massive amount of energy floating around at the time, atop Mount Khrazad (there was a massive gate, like, right there), it just...re-carved the conduit.
- Punundrum - Blue Soul, trades it's aid for puns
- Scorching Heat - Red Soul, a ladies'...dragon? Implanted in Gauthak's neck.
- Winter's Kiss - White Soul, the first Orb the group encountered
- Murder McStabbyStab - Green Soul, aka the "Murder Orb". Likes to Murder.