Companion sketch #11: Steven and Dodo (and HiFi).
Companion sketch #8: some love for the Hartnell era with Oliver Harper (from the Big Finish audios) plus Polly and Ben.
Kyoryuger-Zyuranger weapon swap
once upon a quote (1/∞)
KingRanger, Riki (Chouriki Sentai Ohranger, 1995)
Ian and Barbara did appear in the fiftieth anniversary special. However, due to complications with the timeline, the event had to be erased from the minds of the Doctor, the viewers, and even Steven Moffat.