Instead of a WTH moment its more like a Luke I am your father moment. Something that greatly changes the entire movie and or series. The finale of Star Wars Clone wars season five made me think of that as a Luke I am your father moment. The moment it changes for a character or story dramatically that you don't see coming.
The revelation of Picard as Locutus on TNG definitely comes to mind as game changer in Best of Both Worlds. The scene where in Buffy, the Vampire Slayer where Angel is first revealed to be a Vampire was the first of many game changers in that series
When Matthew Crawley is killed in Downton Abbey.It really sucked and reminded me of Titanic.The guy goes through Hell and ends up dying anyway.
when beezel revealed that he had been living with a lesbian who he thought was going to **** him and had given her like 14000 dollars or something the game aint never been the same
LifeInTechnicolor: Funny you should say Titanic: In the 1970s, there was this British TV series called Upstairs, Downstairs that was a look at the British class system in a aristocratic house in late 19th/early 20th century Britain, between the rich and poor. It was kinda sorta the Downton Abbey of its day, but one of the actresses who played one of the rich people didn't like her part and was always badmouthing the show in the press, wishing she was one of the poor servants instead. So the show's producers wrote her character out by sending her to America....on the Titanic!
Scully getting abducted on the X-Files. It's virtually the true start of the X-Files mytharc. Shane's betrayal on The Walking Dead. While it was blindingly obvious, it still forced a major change in Rick's character. The Red Wedding in A Song of Ice and Fire. I'm not going to elaborate on this. If you don't know what it is, then for your own sake don't Google it.
Actually I would say the change in Rick's character really started when he put a bullet in Walker!Sophia's skull. That was when he really began to take charge in earnest.
Just to name a few (and I'll try to go easy on spoilers)... - "The War Games" on Doctor Who, when we finally learn just who the Doctor is and why he's wandering. - "Special Relationship" on The Sandbaggers, when we see just how far Neil Burnside is willing to go to protect security at SIS. - "Abysinia, Henry" on M*A*S*H, when Henry gets McLeaned. - On Her Majesty's Secret Service, when Blofeld hurts Bond in the cruelest way possible. - And every season finale from Babylon 5 certainly qualifies.
When annoying buttinsky Dale got gutted by a zombie on THE WALKING DEAD. This dried-up, ridiculous-hat-wearing curmudgeonly goody-two-shoes was more plot-killing 'dead weight' on the show than all the zombies combined. Now the character development, and the show in general, is really beginning to pick up steam. Good riddance to plot rubbish.
- "Pressure Point" on Blake's 7, when we find out that when Blake is wrong, the price is very high. - "The Tenth Planet" on Doctor Who, when we first witness regeneration. - Psycho, when Marion Crane gets an unexpected visitor.