MarStarBro is the former director of Vs Sonic.Exe, he was going to be a playable character in the mod who would go up against his own EXE, SL4SH, before being replaced by Boyfriend.
Apollyon is an EXE created by @averyavary and @RblxTrex that appeared in the mod, but it can be assumed that Apollyon was removed when Avery left the team.
Shocker was a concept song, it wasn't supposed to be in the mod, @octigone was just showing it to the devs. he wasn't part of the team, but he knew people who had ties to him and they asked him to do a joke song.
Rosy_ALT was an EXE based on Amy and was planned to appear in the mod, facing off against a Tails, however all that is publicly available is just two concept art and an unnamed teaser song that is part of Leaked 14
Ice Cube is a discarded character that was going to appear in 2.5, but was discarded when the mod was removed. but it will be reused for Soulless DX.
1/3 trivia vs sonic.exe / Right Burst the creator of the mod has confirmed that Soul Tails cannot fly. He is still sweet but he is very shy around other people and he is afraid of sonic.exe
deleted material from vs sonic.exe/ Melthog was going to start in Vs. Sonic.EXE 2.0 / 1.5, but Revie thought it was "too similar to EXE, because it had a fake form", they scrapped it for that and its existence was basically wiped off the internet.