I experienced the same problem many people in the comments experienced, with gallery. All the normal Animations of act 2 and 3 of the 4 gameovers are unlocked after beating the Boss of charter 2 on easy and playing the first 3 Levels of chapter 3 on easy. For the 4th gameover you probably need to beat the Boss of chapter 2 on normal. Some of the unique Animations are not avaible in the gallery at the moment like the batgirl from the chapter2 and the new chapter 3 animationes(Imp) and the new game over (Imp).