Fan sequel
Sonic: Before the Sequel
by LakeFeperd (Felipe Daneluz) · 2013 · Platformer

Fan game set between Sonic 1 and 2, first of a trilogy.
Fan game set between Sonic 1 and 2, first of LakeFeperd's trilogy; only third-party reuploads were found, not the author's own download page.
Built upon Sonic the Hedgehog (1991).