Complex sentence: The doppleganger was also later featured in the "Dungeons & Dragons Game" set (1991), the "Dungeons & Dragons Rules Cyclopedia" (1991), and the "Classic Dungeons & Dragons Game" set (1994).
Split into simpler sentences: The doppleganger was also later featured in the "Dungeons & Dragons Game" set (1991), the "Dungeons & Dragons Rules Cyclopedia" (1991), Various. TSR, 1991 and the "Classic Dungeons & Dragons Game" set (1994).