|Boss||Ashura the Hedgehog|
Forlorn Forest is a dense forest area seemingly stuck in perpetual night, lit by various luminescent plants and insects. However, the forest changes depending on who enters it, becoming decorated with mementos of what the travelers left behind when they died, formed from their memories. All mementos are visible to everyone in Forlorn Forest, not just the ones relevant to that person. Ashura mentions that this area is meant to help the deceased remember the better times as they come to terms with their fate.
During Sonic's travel through this level, various past elements of Sonic games become part of the terrain: Badnik enemies, springs, spikes, small animals, past stage architecture, etc. In addition, pictures of Sonic's friends and enemies can be seen in the background. Other mementos of unknown characters appear throughout Forlorn Forest stages, though some figures can be seen through the trees, implying that these belong to them. Despite Ashura not actually being dead, the forest changes for him as well, likely due to his role in the spirit world, as his boss arena has a stage with large speakers within a clearing.
With six Cross Pearls in their possession, Sonic is led by Nazo to Forlorn Forest, a world of the deceased's memories, in search of the orange Pearl. As Sonic travels through the forest, the sight of all the friends he left behind, as well as the memories of stopping Eggman, cause Sonic's composure to break as he faces a realization that he wanted to deny: Despite risking his life on an consistent basis, he fears his own mortality and the feeling of helplessness, and cannot fully deal with loss. It is one of the few times in the game Nazo drops his attitude and shows genuine sympathy for Sonic.
Upon finding the place where the seventh Cross Pearl is located, Sonic finds the shrine surrounded by a music stage, and a spotlight illuminates Ashura, guitar drawn. Ashura isn't surprised that Sonic refused to back off, but gives him one more chance to give back the Cross Pearls and just accept his fate, declaring death to be a finality that isn't meant to be tampered with. However, all his words do is end up angering Sonic, furthering his resolve to not stay dead, so Ashura stops trying to convince him, battling him with the power of his musical might. Despite a hard-fight battle, Ashura loses to Sonic, leaving the Cross Pearl open for his taking. Ashura warns Sonic that he'll unleash bedlam if the Cross Pearls are gathered together, but Sonic tells him that if he does, it won't last if he's alive again, before leaving the forest behind.
Forlorn Forest does not attempt to utilize a level-specific gimmick mechanic. As the level is based around Sonic's memories, it plays exactly how you would expect a Sonic stage to go: Flowing level design allowing for speed, Badnik enemies to defeat, optional pathways to find hidden items, etc. Performance in this level is entirely due to the player. As the levels go on, familiar architecture from previous Sonic games work their way into Forlorn Forest, such as Green Hill's loops, Marble Garden's giant slopes, City Escape's grind rails, and Press Garden's conveyor belts, alongside background elements taken from stages like Casino Night, Windy Valley, Hang Castle, and Savannah Citadel. Wisps can occasionally be seen in the background, but do not affect the gameplay.
The boss battle with Ashura, like previous battles, puts you in a 3D arena to battle. Ashura will start on his stage and play his guitar, generating sonic wave projectiles in a set rhythmic pattern before they fly at Sonic. Sonic can still move freely, but the projectiles can lead their paths to catch Sonic off-guard if all he does is run straight. Ashura can't be attacked unless Sonic breaks the speakers nearby, at which point he leaps off to battle you himself, trying to swing his guitar at you and essentially using the Homing Attack as a projectile, leaping into the air with a spin before sending out a sonic orb. As Ashura takes damage, he adds new attacks, such as a 360-degree sonic wave as a barrier or rapid-fire blasts from a hammer-on technique.
- Forlorn Forest is one of only two areas in Sonic Afterlife to have Badniks as enemies, the other being Factory Freakout.