Hyudoros are ghosts with a horrific appearance, that reside in dark places. In Sonic & Knuckles, they are presumably ghosts of starving animal friends inside the single Capsule. As they start appear they are shown to be small ghosts, but as the lights start turn off, they grow two horns on their head and have black void eyes.
Sonic & Knuckles
In Sonic & Knuckles, the player encounters the Hyudoros in Sandopolis Zone Act 2, after the player opens a lonely Capsule. Hyudoros cannot be destroyed; if the player jumps, they follow him. If the player goes too fast, they disappear and meet him wherever the player is. They don't try to hurt the player until it is completely dark. The player also can't touch them as they fly above until they are in their perfect form.
Hyudoros appear in three different forms, depending on how dark it is. The darker the act becomes, the stronger the Hyudoros will be:
- In full light, there are no Hyudoros.
- In semi-brightness, one small Hyudoro appears to be floating above.
- In semi-darkness, two evil-looking Hyudoros appear hovering, while they don't start attacking.
- In complete darkness, three Hyudoros with horns on their heads appear and start to attack the player.
The only way to make the Hyudoros disappear for a while is to pull down the light switches located around the level. The Hyudoros disappear completely and the lights go on when the player falls into the arena where the boss of zone is encountered. The player Spin Jumps on them during the attack, but reappear right after a second and continue their assault. If the player is invincible then a similar effect will occur. As Knuckles the Echidna, the ghosts seem to already be free, since Sonic opened the capsule earlier. This is especially dangerous at the beginning of Act 2, since the act starts off completely dark and Knuckles has no Rings.
Sonic Rivals 2
In Sonic Rivals 2, the Hyudoros appear as enemies in the Mystic Haunt Zone. In this game, only one Hyudoro appears during one mansion section of the level. The player might not be able to defeat the Hyudoro himself but it is possible to make it disappear by pressing down the button before the Hyudoro attacks.
In other media
Sonic the Comic
In the Sonic the Comic series published by Fleetway, the Hyudoros are ghosts inhabiting the Lost Pyramid of Sandopolis. As a part of the pyramid's curse, they will attack any intruders when the light starts to fade. During the comic's run, they attacked Captain Plunder and his crew when they tried to steal the pyramid's treasure and the Chaotix Crew when they paid a visit.
- As the Sonic Jam strategy guide states, Hyudoros weren't created by Dr. Eggman. It also reveals that Eggman infiltrated into the pyramid and trapped the ghosts inside the Capsule, working very hard.
- Several media mentions that Sandopolis Zone Act 2 takes place in a cursed pyramid, with Dr. Robotnik trying to trap Sonic inside.
- When the capsule is opened inside of pyramid, it releases six Hyudoros even though only three of them start to follow the player. It is unknown where the three others have gone, although it is possible that as one of Hyudoros disappear, another one comes to take place.
- In Sonic the Hedgehog 3, even though players can avoid opening the capsule containing Hyudoros with Debug Mode or glitching, they still appear when players touch any Checkpoint.
- Hyudoros and Boos are considered to be separate ghost species, but there are a few similarities. Both of them have resided in a dark pyramid and are able to disappear and come back.
- Three Hyudoro make an appearance in the Sandopolis Zone sub-area of the Sonic the Hedgehog World in LEGO Dimensions. As in Sonic & Knuckles, they appear after opening a lone capsule. Upon being freed, they split a Gold Brick into three pieces and hide in dark corners of the map. The player must use the Shift Keystone to get near their hiding spots, then push a switch to open the doors they hide behind and defeat them using a character with the Illumination ability.
- ↑ Sonic The Comic Issue #43 (Sonic & Knuckles Special Part 1)
- ↑ "Here's the desert stage, something that hadn't appeared in the series until this point, so we were able to make it relatively free of earlier influences. The ghosts appearing in the second half are the first enemies who weren't made by Eggman. When he infiltrated the pyramid, he must have worked very hard to trap them inside that box." - Takashi Iizuka, Sonic Team Commentary in Sonic Jam Strategy Guide.