(I’m pretty sure a comparable trope for this has to exist already. But until someone tells me what it is, I’m going to assume I’m the first one to come up with this idea.)
This trope was inspired by an article on ComingSoon.net concerning “Spider-Man 3” titled: “Venom: The Ten Minute Villain?”
This trope refers to a villain that only appears at the end of a film, and then only for a couple minutes before he/she is killed. In other words, a “ten minute villain”. This is usually the result of too much fanservice or an inability of the filmmakers to decide on a proper villain, particularly in comic book films. However, it can occur elsewhere too.
Specifically, to be a Ten Minute Villain, you must be a villain who only becomes a villain (i.e., a distinct credible threat or conflict to resolve) within a short period before the conflict is resolved. Hence, Venom in “Spider-Man 3” was a Ten Minute Villain in spite of Eddie Brock being in most of the movie, as he wasn’t a threat until he wore the Black Costume. However, Talia Al Ghul in “The Dark Knight Rises” was not a Ten Minute Villain but was the Woman Behind The Curtain. The threat she represented never changed…it was simply revealed Bane was working as her puppet. Hence, if a conflict is present the whole story but one simply doesn’t know who is behind it until the last ten minutes, it doesn’t count.
“Spider-Man 3” – Venom
“Mortal Kombat” – Reptile
“Final Fantasy VII: Advent Children” – Sephiroth
“The Dark Knight” – Two-Face
“X-Men 2” – Magneto (In the sense that he generated the final threat)
“Final Fantasy IX” – Necron
“Transformers” – Megatron (He counts because the Decepticons themselves were the main threat before he thawed)
“Frozen” – Hans