Prelude to a Twist?
Because when you really think about it, a Wham Episode is basically a twist that changes the entire face of the story or what not. Plus, it's an Incredibly Lame Pun
Innocuously Important fits the description, and seems to fit all of the examples. Prelude To A Twist sounds more specific, since many of the examples (including the Trope Namer) appear to be reference points not just for a later plot twist but for later general plot arcs.
Chekhov's Episode seems like a good pick, as this isn't a bad choice to snowclone for thematic reasons.
Some trope name involving First Domino might work, the idea that this is the event that put everything else into line, you just didn't notice. Or maybe Retroactive Twist.
Who needs a signature, really?^This (as a matter of fact, I was about to suggest it myself). Or Wham Preparation.
I was browsing through the examples and I'm a little confused as to what separates this trope from just being "An episode that contains one or more Chekhov's Guns". Just getting this straight...it's an episode whose significance to the arc isn't evident (to the point that it could be mistaken for filler or a Breather Episode) until a later episode reveals its true importance?
Could probably use a clearer description.
Crowner
. (I think I got all the suggested names.)
edited 27th Oct '10 5:58:35 PM by sgrunt
This space for rent. Cost: your soul.I edited Inocuously Important to Inocuously Important Episode...so that I could vote for it. Overly broad otherwise.
Searching for plausible mechanisms.Bump to draw attention to the above and hopefully improve the vote spread?
This space for rent. Cost: your soul.It's still there... it's just that the link in the header is wrong. Try Midnight On The Firing Line.
Also, it looks like we have a preferred name to rename to at this point.
This space for rent. Cost: your soul.
Crown Description:

Innocuously Important is good. I don't think this quite fits the Crouching X Hidden Y snowclone, which is mostly characters anyway.
The child is father to the man —Oedipus