|First level, Sonic Forces|
|Level theme: tropical island|
|Secondary level theme: desert/western|
|Played as: Sonic, Shadow (DLC)|
Lost Valley is the first stage of Sonic Forces, which is based on Green Hill Zone from Sonic the Hedgehog, but with greater influence from Green Hill (Sonic Generations) of Sonic Generations. At this stage Sonic discovers that the dazzling landscapes of these tropical hills were destroyed by the industrialization imposed by Dr. Eggman, the landscape now turned into a larger desert with dead and dry vegetation.