2-04: Mirror, Mirror
A transporter accident swaps Kirk, McCoy, Scotty, and Uhura from distinctly opposite parallel universes.
2-16: The Gamesters of Triskelion
Kirk, Uhura, and Chekhov are abducted and forced into combat games with other captives.
2-24: The Ultimate Computer
The Enterprise's test of Dr. Daystrom's greatly enhanced computer becomes deadly.
2-20: Return to Tomorrow
Several crew members are possessed by advanced non-corporeal beings.