Sonic the Hedgehog (Prototype) - Hidden Palace

A prototype of Sonic the Hedgehog for the Sega Mega Drive.

Sonic 2, iOS & Android

A Quest for the Secret Origins of Lost Video-Game Levels - The Atlantic

The First ROM Dump of a Sonic 1 Prototype Has Finally Been Released Thanks to Hidden Palace « SEGADriven

Sonic the Hedgehog 2 (PROTOTYPES) LOST BITS Cut Content & Unused Zones [TetraBitGaming]

A brief history of Sonic The Hedgehog on PC

Hidden Palace Zone (Sonic the Hedgehog 2), Sonic Wiki Zone

Lost Hidden Palace Zone (Classic/Rem [Sonic Mania] [Works In Progress]

The Sonic & Knuckles beta cartridge shows truly what SEGA is doing. They want Sonic to be more than an icon. If he's in our reality, fun will TRUELY be infinite. Don't

Sonic The Hedgehog 2 BETA Showcase on BETA-Talkers - DeviantArt

Sonic the Hedgehog 3 (November 3, 1993 prototype) Soundtrack

Hidden Palace Zone - Sonic Retro

Hidden Palace Zone - Sonic Retro

SEGA Sonic the Hedgehog Prototype Game Build from 1991 Surfaces, Here's a First Look - TechEBlog

A story that gave a developer a pirated version of Sonic the Hedgehog 2 to developer Yuji Naka - GIGAZINE