Any specification about the size? The size determines everything. There are many ways to do this. One single frame with both of them in it that is about (500 x 300) pixels, or separate face shot of each of them that's (150 x 150) pixels, not sure but I think that's the size or the mobs in the forest. Once one of them goes down, their picture is replace by the one in Kyuubi Mode (300 x 300) pixels. Since both of them have similar features to each other, both of them will switch to the same Kyuubi Mode picture when the other gets KOed.