Sonic's Timeline SRB2 Message Board

First of all I'll mention I wont count spinoffs as mainline cannon games (Sonic Rush, Mobile Sonic games, Sonic Racing games) I'll count the storybooks as the gameplay has kind of a development of an early boost (although as someone who played them I must say that those boosts were crappy)

NES Sonic SRB2 Message Board

Sonic Robo Blast 2 PSP - GameBrew

Prerelease:Sonic Robo Blast 2 - The Cutting Room Floor

Release] Sonic Robo Blast 2 for New3DS, Page 3

Advance Sonic SRB2 Workshop

Prerelease:Sonic Robo Blast 2 - The Cutting Room Floor

Sonic Robo Blast 2-D — Greenflower Zone by joshyflip on Newgrounds

Sonic Robo Blast 2 (3D Sonic fangame in development for 20+ years) releases huge new update. [New July 2020 update.], Page 10

Splice The Hedgehog (RPG Fangame), Sonic Fanon Wiki

Sonic 3D SRB2 Workshop

SegaSonic the Hedgehog - Debug Tools and So Much More