S01:E01 - Planet 46
Fireball XL5 intercepts a planetomic missile sent to destroy Earth. On Planet 46 Steve and Venus are captured by the Subterrains who promptly launch a second missile, with Venus on board.
S01:E12 - The Last of the Zanadus
A friend of Steve's returns from a 10-year space expidition and is unaware that he is under mind control to the last of the Zanadu people who have sworn revenge on the Lazoons.