Play as Yoshi and have all the characters. Jump into the picture, select the star you want, and go. Once there, go to the place with General Goomba (Goomba with the Wario cap), Major Goomba (Goomba with Mario cap), and Lieutenant Goomba (Goomba with Luigi cap). Get near the fence and they will either run from you into the fence and kill themselves, or run to you and then commit suicide. Note: These are easiest with General Goomba.