Here's one I've had recently, in certain cutscenes you get to make a choice between two characters, the one you were playing as and another and this choice determines who you play as in the coming boss battle, of course you can't intentionally chose the person you want to lose and make them lose, you can only progress in the story by winning.
The first character (the one with the longest possible story) is the weakest character to play as but to get the happiest ending that's who you have to play as the entire way through, whereas the characters thereafter will be increasingly more powerful but have increasingly dark motivations which result in ever more depressing endings, although getting to play as them is neat because it gives you a chance to explore their motivations and uncover the depth of their personalities.
This mechanic can also be somewhat subverted by for example having the character you were playing as mortally wounded, but he's a vampire and can regenerate by draining the life of a friend, but if you chose not to he will fall into that stasis sleep vampires do and the character you saved will become the one you play as, leading to a happier ending than if you'd gone down the selfish path.
