Doctor Eggman Nega

Eggman Nega (ドクター・エッグマン Egguman Negau) is the third most recurring villain in the Sonic game series and has been the main villain and final boss of all three games he's been in: Sonic Rush, Sonic Rivals, and Sonic Rush Adventure. He is the primary nemesis of Blaze the Cat. His design appears reminiscent to the older Eggman from the Genesis Sonic games, albeit with the colors reversed.

In the Sonic Rush series, Eggman Nega is introduced as an extra-dimensional counterpart of Doctor Eggman from Blaze's home dimension. He is more cruel and calculating than the Eggman from Sonic's world, although the two often work together, and he has sent Blaze's world into ruin, which is why he sets out for the Sol Emeralds. He is eerily polite for such a cold and calculating person. His downside, however, is that he can sometimes lose track of important details while making unnecessary speeches.

While Eggman himself is first thought to be the primary antagonist in Sonic Rivals, the player soon finds out that Eggman Nega has captured Eggman and is disguising himself as him. Sonic Rivals also reveals that Eggman Nega is from 200 years in the future (which fits in with Sonic the Hedgehog, which reveals that Blaze is from the future as well) because this alternate universe has its own time zone. Using a special camera, he turns several objects and characters into cards, with the objective of turning the world into a card that he will be able to control. During the somewhat ambiguous ending of the game, Nega is captured inside a card of his own by Silver, yet it was never revealed how he returned to the past.

Personality
Eggman Nega is eerily polite, despite being even twice as cruel and calculating than Dr. Eggman himself. He appears to be insane, trying to destroy the whole world along with himself on numerous occasions. He has also been described as very sneaky, even disguising himself as Eggman on some occasions. His downside, however, is that he can sometimes lose track of important details while making unnecessary speeches.

Doctor Eggman
Eggman Nega's ally and enemy is Dr. Eggman. The two worked together in Sonic Rush and Sonic Rush Adventure. This is possible because they both have the same goal of ruling the world. Yet, they work together again at the end of those game to try and defeat Burning Blaze and Super Sonic, only to be defeated by them in the end. However in Sonic Rivals Nega turns on Eggman, by turning him into a card. Eggman later helps Shadow and Silver to stop Nega by flying them onto Nega's moon base. In,Sonic Rivals 2 Eggman Nega tries to power and awaken a inter dimensional monster called "Ifrit" to destroy the world by using the Chaos Emeralds and the Chao to do it after reading old files of Professor Gerald.

Blaze the Cat
One of Eggman Nega's main foes is Blaze the Cat, who guards the Sol Emeralds. They are both from the same world and it is suggested that Eggman Nega is the equivalent of Sonic's Dr. Eggman. Much to his amusement, Blaze loses her composure easily with him, as shown at the end of Sonic Rush Adventure when Nega threatens to destroy her kingdom. As Blaze has not appeared in the Rivals series, it can be assumed that she is unaware of Nega's "descendant" origin.

Silver the Hedgehog
Another one of Eggman Nega's foes is Silver the Hedgehog. In Sonic Rivals, it is revealed that the two are enemies, and Silver is one of the few characters in the game that knows that Nega is actually disguising himself as Eggman. Silver battled Eggman Nega, however Nega's device malfunctioned, and he himself was turned into a card. They clash again in Sonic Rivals 2. Silver seems to be unaware of Nega's "Dimension" origin but since this origin isn't discussed in the Sonic Rival series it is unclear if Silver has any knowledge of Nega's Dimensional origin.

Sonic the Hedgehog
In Sonic Rush, Sonic becomes enemies with Eggman Nega, chasing him through each zone, trying to find out who he is and what's going on. Nega hasn't really talked to Sonic much, just to introduce himself at the start of Sonic Rush, and at the end of Sonic Rush Adventure when Eggman and Eggman Nega appear at the end. They also clashed in Sonic Rivals and Sonic Rivals 2, but Sonic never saw through Nega's disguise in these games. Because of this, Sonic is unaware of Nega's "descendant" origin or his involvement in the Sonic Rivals Games.

Metal Sonic
Eggman Nega also had a temporarily ally in Metal Sonic. It is unexplained why Metal Sonic worked with Eggman Nega, but the alliance ended after Sonic Rivals. In Sonic Rivals 2, not only are Metal Sonic and Eggman Nega enemies, but Nega provides Metal Sonic with his own personal rival. Apparently upgrading Metal Sonic's design, Eggman Nega created Metal Sonic version 3.0. This Metal Sonic copy looks exactly like the original Metal Sonic, but has a black and yellow color scheme, similar to Gemerl of Sonic Advance 3.

Shadow the Hedgehog
Sonic Rivals 2 also features an enmity between Eggman Nega and Shadow the Hedgehog. Shadow learned of Nega's identity and plans in the first Rivals, and is quickly caught on to his disguise as Eggman in the sequel. Shadow and Metal Sonic both work together to stop Eggman Nega from releasing the Ifrit and destroying the world. Shadow seems unaware of Nega's activities in the Rush series, including his "dimension" origin.

Rouge the Bat
Also in Sonic Rivals 2, Nega has some kind of connection with Rouge the Bat, who he hired to find the Chaos Emeralds for him. However, Rouge was unaware of her client's identity and came to believe it was Dr. Eggman who had hired her. Her part in Sonic Rivals 2 means that she was unwitingly working for and against Eggman Nega.

Knuckles the Echidna
Knuckles and Eggman Nega both appeared in Sonic Rush, but they never really encountered each other. Nega clashed with Knuckles directly in Sonic Rivals, but Knuckles never realized that Nega wasn't the real Eggman. When Knuckles allies with Rouge in Sonic Rivals 2, he could be considered to be working both for and against Nega.

Espio the Chameleon
When Espio was assigned to uncover the recent Chao-Nappings, he came across Silver, and later met Eggman Nega. He and Silver joined forces to battle him. Nega did whatever he could to kill the duo, but all of their attempts failed. As he sent out Metal Sonic 3.0, Silver and Espio made progress defeating it after a long harsh battle in the Ifrit's lair. The team also recovered the lost Chao from him and as Nega was suddenly stuck under rubble inside the cave while the door was closing them in asking for help, Espio answered back saying, "You reap what you sow, Eggman Nega." Silver and Espio then escaped with no problem as the door closed.