2-01: Amok Time
When Spock exhibits irrational behavior from pon farr, The Enterprise heads to Vulcan for help.
2-04: Mirror, Mirror
A transporter accident swaps Kirk, McCoy, Scotty, and Uhura from distinctly opposite parallel universes.
2-20: Return to Tomorrow
Several crew members are possessed by advanced non-corporeal beings.
2-22: By Any Other Name
The Enterprise is commandeered by members of the Kelvan empire, seeking to return to the Andromeda galaxy.