In the many DRACONIA universes, The Heartful are just as evil as the Heartless.

Heck, the only differences between them is that while the Heartless are based on darkness, Heartful, in contrast, are based upon light.

Then there's the Hearthorror: beings based on both light and darkness at the same time.

Needless to say, they're very powerful.

What Kar-J said.

While Giant Heartless vanish in light, I assume Heartful vanish into darkness, and Hearthorror into sparks like the Nobodies do.
Also, for some reason all Hearthorror are capable of exhaling very poisonous gases toxic enough to even bypass normal gas masks; basically Dariian gas masks are required as well as HAZMAT suits or the feminine Immortality Armor (for some reason the Immortality Armor worn by guys are useless against that unless the wearer is also a Cypher like Shaun or Xeshan, or a Nobody like Kingdom Hearts-Roxas or Axel). Even undead are affected by the gas, as well as those that don't need oxygen; it melts bones and skin and flesh. Force fields are also useless, as is hiding from the gas (the gas is capable of going through walls and such).
On Karjams, though, the gas has an entirely different effect, regardless of whether they use their mimicking ability or wearing Dariian gas masks with HAZMAT suits; it won't kill them but it will disable all their abilities no matter what, without killing them at all. And it's even in the laws of the Dariian galaxy. (So the Purple Karjam would basically have no powers in the Dariian galaxy for a week if he inhales the gas for just a minute.)

Hearthorror exist when Heartless and Heartful, who are natural enemies, suddenly co-exist peacefully as allies.
Hearthorror are basically stronger than Heartless and Heartful combined.

All that from what TED told me in April this year, via PM.