For whatever reason, sometimes I am only able to find one card of certain players. To be considered a One-Card Wonder, a player must have been active since 1991 (when I started paying attention).
The only Red Sox card of Ernest Riles in existence is this 1994 Fleer card. Riles spent one year with the Red Sox in 1993. He was a utility infielder, spending time at second base, third base, first base, and designated hitter, and he was used a pinch hitter and pinch runner. Riles was a steady defender, but was not much with the bat. He did manage to pop five home runs, but his slash line was .189/.292/.350/.641. Riles made it into 94 games that season, but only had 170 plate appearances. He bounced around the minors for a couple more seasons after 1993 before calling it a career.