Sprite comparison for Mania's intro animation (SegaSonic, Sonic 1, 2 and CD) : r/SonicTheHedgehog

RetroSpective - Sonic the Hedgehog 2 - Rings & Coins

Sonic the Hedgehog, The Codex Wiki

What's Your Favorite sonic Design? (Mines Sonic 3) : r/SonicTheHedgehog

New and Cartoonish Sonic Sprites (Sonic 1)

Sonic Prime The Chaos Project: Sonic the Hedgehog

Sonic The Hedgeblog — Comparison of Sonic's rotating running animations

Sonic the Hedgehog 2 (Sega Master System, Game Gear) - The Cutting Room Floor

Sonic the Hedgehog – Page 2 – Wizard Dojo

Sonic The Hedgehog Compilations - Every Sonic Collection Before Sonic Origins

Sonic The Hedgehog Edited V4 by CartoonsAnimate22 on DeviantArt

The extraordinary fan-game roots of Sonic Mania - GameCrash