Sonic Rivals

5D perspective. Characters race to the finish line while avoiding the level's obstacles. The game contains six zones, each with three respective acts, the third being a boss battle, totaling in 17 stages. Boss battles at the end of levels require the player to defeat the boss before the competing character does.

Five different characters are playable; Sonic the Hedgehog, Knuckles the Echidna, Shadow the Hedgehog, Silver the Hedgehog, and Metal Sonic, but gameplay is identical for all characters. The game features power-ups to collect that offer additional offensive and defensive abilities.

When the mysterious Onyx Island appears out of nowhere, Sonic and Tails fly there to investigate. They confront Doctor Eggman, who reveals his latest device: a camera which can turn people and things into cards, having already done so to Amy. He turns Tails into a card just as Knuckles arrives, angry at Eggman for using his device on the Master Emerald as well. Eggman announces his plan to conquer the world by turning everything to cards, challenging Sonic and Knuckles to stop him as he flees.

The two heroes both set out independently to stop his plan. Elsewhere, Shadow receives a distress signal from Eggman, but upon finding him, the doctor denies sending one. He later receives a communication from Rouge warning him she has stumbled upon a dangerous secret about Eggman, but she is turned to a card before she can continue. Suddenly, Silver appears from the future, and tells Shadow he needs to get to Eggman first.

Sonic Rivals was developed as a collaborative effort between Sega and Backbone Entertainment for the PlayStation Portable (PSP). The game's concept originated from a traditional platform game Backbone designed. Takashi Iizuka became involved with the game, and he changed its direction to a racing game. The majority of development was handled by Backbone with assistance from Sega Studio USA, although some aspects, such as the story, were done by Sega. The developers chose to create the game on the PSP over the Nintendo DS, due to its stronger processing power and higher graphical quality.

According to producer Taylor Miller, the goal of the developers was to return to the gameplay style of the original Sega Genesis Sonic games, but with new elements such as competition. In designing the stages, Sega provided Backbone with level design maps from all the 2D games as a reference, and Backbone looked to all games up to Sonic Rush for inspiration. Building alternate paths—a common feature of the original games—was cited as challenging, with the goal of allowing as many rivalry interactions as possible. In choosing playable characters, Backbone focused on characters who maintained the biggest rivalries in the Sonic franchise, such as Sonic and Shadow.

Sonic Rivals received "mixed or average" reviews from critics, scoring a 64/100 on Metacritic, and 66.17% on GameRankings. Both it and Rivals 2 were later re-released in North America and Europe as part of the Greatest Hits and Essentials lines respectively, indicating over 250,000 units were sold by the end of 2007, as well as part of the Double Rivals Attack Pack! on October 18, 2011.

Reviewers consistently praised the game's presentation. Juan Castro of IGN wrote that the game had tons of "graphical flourishes" that made it belong on the handheld, a sentiment shared by Greg Mueller of GameSpot. The music received similar praise, with GameSpot finding the music upbeat, although GameSpy said it was "nowhere near as good" as previous games in the series.