Sonic Artchiveさんのイラストまとめ

Various pieces of artwork of Sonic skiing from the Sonic Adventure Stylebook
(illus. by Yuji Uekawa)

Character marks for Sonic, Tails, Amy, and Knuckles from the Sonic Adventure Stylebook
(illus. by Yuji Uekawa)

Concept art of various places (Camelot Castle, Deep Woods, Faraway Avalon, and Molten Mine) for Sonic and the Black Knight
(illus. uncredited)

Early art of Sonic and Shadow for Sonic Battle, depicting a different yet similar style to the one seen in the final game
(illus. by Hisanobu Kometani?)

Promotional artwork depicting Sonic, Tails, and Knuckles for Sonic Jam (SEGA Saturn)
(illus. by Satoshi Okano)

Various pieces of promotional art of Sonic for Sonic Rush Adventure
(illus. by Yuji Uekawa)

Different pieces of key art featuring Sonic, Tails, Knuckles, Amy, and Cream for Sonic Advance 3
(illus. by Yuji Uekawa)

Concept design sheets of Amy Rose for Sonic CD
(illus. by Hisashi Eguchi; taken from Sonic Origins)

Artwork featuring various unnamed characters, an early design for Dr. Robotnik, and Sonic's scrapped girlfriend Madonna.
Made during the development of Sonic the Hedgehog (1991)
(illus. by Naoto Ohshima; taken from Sonic Origins)