Re: The most mediocre episode?
Meh is probably a good word, though I'm from a generation before it came into general use, so don't fully understand the meaning. But that sounds close. An episode so forgettable, it made no impression on you at all.
Well we do tend to remember the best and the awful. For those that are sort of so-so as you say it makes no lasting impression.
On the continent of wild endeavour in the mountains of solace and solitude there stood the citadel of the time lords, the oldest and most mighty race in the universe looking down on the galaxies below sworn never to interfere only to watch.