Hyudoro

Hyudoros (ヒュードロ in Japan) are ghost enemies which first appear at second act of Sandopolis Zone in Sonic & Knuckles. They are basically ghosts of beings inside of Egg Capsule, which got free by the player and apparently starts to attack as the zone got completely dark.

Description
Hyudoros are ghosts with horrific appearance that usually exist in dark and ghastly places for example inside of pyramid of Angel Island. In Sonic & Knuckles, it is possible that Hyudoros might be ghosts of starving animal friends inside of the single capsule. These ghosts in the game appear in three different forms, depending on how dark it is. The darker the act, the stronger the Hyudoros will be:


 * 1) In bright, there are no Hyudoros.
 * 2) In semi-bright, one small Hyudoro appear to floating above.
 * 3) In semi-dark, two evil-looking Hyudoros would appear floating above but even yet, they don't start do anything.
 * 4) In completely dark, Three Hyudoros with horns on their heads would appear and starts eventually to attack towards to the player.

Sonic & Knuckles


In Sonic & Knuckles, the player encounters the Hyudoros at second act of Sandopolis Zone after the player opened a capsule. Hyudoros cannot be destroyed, as if the player jumps, they follow him. If the players go fast, they disappear and meet him where the player ever is. They don't try to hurt the player until it's completely dark. The player also can't touch them as they fly above until they are in their perfect form.

The only way to make the Hyudoros disappear for while is to pull down the light switches located around the level. The Hyudoros disappear completely and lights go on when the player falls to the arena where the boss of zone is encountered.

As Knuckles the Echidna is playable in Sandopolis Zone Act 2, the ghosts seem to be already free, since Sonic first opened the capsule. Hyudoros act identically through the entire act until to the boss arena.

Sonic Rivals 2
After many years, Hyudoros do reappearance in Sonic Rivals 2. They appear as enemies at the Mystic Haunt as there are this time only one Hyudoro at one mansion section of the level. The player might not able to defeat the Hyudoro himself but is possible to make it disappear by pressing down the button before Hyudoro's attacking.

The boss of the Mystic Haunt appears to be big variation of Hyudoro with horns and piloted by Eggman Nega as it is referred to as the "Egg Phantom". Like normal Hyudoros, its weakness reveals to be lighting.

Sonic the Comic
In Fleetway's Sonic the Comic Hyudoros are mentioned as Sandopolis Ghosts, and appear only at issue 48 story Mystery of the Sandopolis Zone. Captain Plunder, Filch and the Per'fessor attempt to leave the pyramid with several bags full of its treasure, while Sonic is going to chase them while Knuckles stops him,  knowing the hazard of pyramid. As the place gets dark, small ghosts starts to follow Plunder and others as Filch saw them and tries to warn them, but Plunder and Per'fessor don't see them. After that three ghosts appear in front of them as Filch believes them to be 'the wrong sort of ghosts', and the leering phantoms chased the pirates out of the pyramid, which sealed shut behind them.

Sandopolis Ghosts have sort of different appearance comparing to its game counterpart, as it normally appears to be small blob, it eventually becomes full form with more sinister look and full body of cloaked phantasms with arms.

Trivia

 * As Hyudoros in Sonic & Knuckles originally came from capsule, there hasn't been have any certification of how they were contained or why.
 * As the capsule opened inside of pyramid, it releases six Hyudoros even trough only three of them starts to follow the player. It is unknown where three others have gone, although it is possible that as one of Hyudoros disappear, another one comes to take place.
 * As the Sonic Jam strategy guide states, Hyudoros are the first badniks not to be created by Doctor Robotnik.
 * Hyudoros and Boo / Boom Boo are considered to be separate ghost species, but there are few similarities. Both of them have resided in the dark pyramid and are able to disappear and come back.