Shadow the Hedgehog could be coming to Sonic Frontiers, according to hints by the developers - Video Games on Sports Illustrated

Ranking Every Mainline Sonic The Hedgehog Game - Game Informer

Do you think Sonic Frontiers will be any good or will it be another disappointment like Forces? : r/SonicTheHedgehog

Playable Shadow is PERFECT in Sonic Frontiers

Sonic Frontiers – Parry Everything

Sonic Team Wants To Make Another Game Featuring Shadow the Hedgehog

How Sega killed Sonic the Hedgehog and made a surprisingly sincere game - Los Angeles Times

WHY SHADOW ISN'T IN SONIC FRONTIERS

Sonic the Hedgehog, Tropedia

Ian Flynn - News - IMDb

Sonic Adventure (Video Game) - TV Tropes

Sonic the Hedgehog Sonic News Network+BreezeWiki

Sega Genesis and NEC TurboGrafX were around even until Sonic came out.