Sonic Forces is a 2017 platform game developed by Sonic Team and published by Sega. It was produced in commemoration of the 25th anniversary of the Sonic the Hedgehog franchise. Sonic the Hedgehog joins a resistance force alongside Classic Sonic, his past self, and the Rookie, a survivor of Eggman's attacks. Together they must stop Doctor Eggman, who has conquered most of the world alongside Infinite, a new enemy, who wields the power of the Phantom Ruby, and is able to create limitless numbers of illusionary clones of past villains. It features three gameplay modes: "Classic", side-scrolling gameplay similar to the original Sega Genesis Sonic games; "Modern", 3D gameplay similar to Sonic Unleashed (2008) and Sonic Colors (2010); and a mode featuring the "Avatar", the player's custom character. Development of Sonic Forces began after the release of Sonic Lost World in 2013. The game's title was chosen to signify its themes of power, teamwork, and armies. The game was intended to have a darker tone compared to previous entries in the franchise, and the character creation system was inspired by Sonic fan art the developers had come across over the years. The game was primarily developed by staff who had worked on Sonic Colors and Sonic Generations (2011), using an updated version of the Hedgehog Engine, used in Sonic Unleashed and Generations. It was announced, alongside Sonic Mania, under the working title of Project Sonic 2017 during the Sonic 25th anniversary event at the 2016 San Diego Comic-Con. Through Sonic Mania entered development years later than Forces, it affected the development, so the games have connected plots. Sonic Forces was released for Nintendo Switch, PlayStation 4, Windows, and Xbox One in November 2017. The game received mixed reviews from critics. They praised its presentation, music, voice acting, character creation system, and the Modern Sonic gameplay, but criticized the plot, overly scripted level design and gameplay, technical problems, short length, and the inclusion of Classic Sonic. Many critics called it a disappointment in the wake of the positively received Sonic Mania, released earlier that year. The critical feedback influenced the development of the Sonic series' next entry, Sonic Frontiers (2022).