Decoy Protagonist: Basically, why should I care if the protagonist has to be killed off and never revives, and then "replaced" by another protagonist. The Hero shouldn't die in the middle of the scene, unless he's Back from the Dead shortly after that. There are other ways to spice up the story.
Suicide Pact: Suicide, even when they commit together, definitely one of most senseless and stupidest deaths for me... Unless if this trope is either subverted and averted into much more positive ones.