Sonic Mania Plus

Sonic Mania is a side-scrolling platformer similar to the early Sonic the Hedgehog games released for the Sega Genesis and Sega CD. Players select one of three playable characters, each with unique abilities: Sonic can perform a "drop dash" which sends him rolling in a dash after a jump, Tails can fly and swim, and Knuckles can glide and climb walls. As with Sonic 2 (1992) and Sonic 3 (1994), players can play as Sonic and Tails simultaneously, or a second player can control Tails independently. Unlockable options include Sonic's abilities from Sonic CD (1993) and Sonic 3 in place of the drop dash, and the ability to control any character alongside Knuckles.

Sonic Mania takes place over 13 levels, called zones. Eight are "remixed" from previous games, such as Green Hill Zone from the first Sonic (1991). Remixed stages consist of new elements and elements from past games. Each zone is divided into two acts, in which the player must guide their character past enemies and obstacles to reach the end.

After the events of Sonic & Knuckles, Sonic and Tails detect a powerful energy reading on Angel Island and board their biplane, the Tornado, to investigate. However, Dr. Eggman sends an elite group of EggRobos to reach the signal before Sonic and Tails. The EggRobos excavate the source of the signal, a magical gemstone called the Phantom Ruby, just as Sonic and Tails arrive. The EggRobos gain new powers from the ruby, becoming the Hard-Boiled Heavies, and send Sonic, Tails, and the island's guardian, Knuckles, through zones the trio have previously visited where they pursue Eggman to prevent him from using the ruby's power for evil, clashing with him and the Heavies along the way.

Sonic and his allies discover that Eggman has used the Phantom Ruby's power to retake control of Little Planet from Sonic CD. They board Eggman's robotic fortress, defeat him and the Heavies, and escape just as it explodes. If all seven Chaos Emeralds are collected while playing as Sonic, the Phantom Ruby transports him and Eggman to another dimension. There, the Heavies' leader, Heavy King, betrays Eggman and takes the ruby, imbuing himself with power; Eggman attacks the Heavy to try to reclaim it.

Development of Sonic Mania began in 2015, led by Australian programmer Christian "Taxman" Whitehead. Whitehead was a prominent member of the Sonic fangame community, and had previously been contracted by Sega to develop remastered ports of Sonic the Hedgehog, Sonic 2, and Sonic CD for mobile phones. After developing the game for a few months, Whitehead presented a prototype, which he called Sonic Discovery, to series producer Takashi Iizuka. Iizuka was receptive, and suggested that it should include old levels from the early Sonic games it was inspired by, "remixed" in a way that felt new.

He also gave it the working title of Sonic Mania, which stuck after no one suggested a better one. The title referenced the development team's "maniacal" fandom for the series; Iizuka described the project as being made "by the mania, for the mania", and as a "passion product" driven by the fans' love for the early Sonic games.

Sonic Mania was announced following years of mixed reviews for the Sonic franchise. According to the International Business Times, the series had been "tarnished by years of sub-par games with only the occasional gem". The Business Times predicted that Sega's approach of releasing Sonic Forces and Sonic Mania in the same year, catering to new and old fans, could repair the series' reputation and lead to a "Sonic renaissance". Several critics expressed excitement for a return to the style of the early Sonic games, and wrote that Sega's previous efforts to develop games in the "classic" style, such as Sonic the Hedgehog 4 in 2010, had been disappointing.

According to the review aggregator site Metacritic, Sonic Mania received "generally favorable" reviews. It became the best-reviewed Sonic game in fifteen years, and several critics described it as one of the best 2D platform games. At launch, Sonic Mania was the bestselling Switch game, outselling Minecraft and Overcooked: Special Edition. It greatly increased Sega's third-quarter profits, and helped Sega almost double sales of packaged games compared to the same period in 2016. By April 2018, it had sold over one million copies worldwide across all platforms.