To get to Scene 23.5, you have to break the tile set off alone in the bottom right in scene 23 two times. The real purpose of this scene is to find Ancardia, it's randomly hidden in one of the chests. However, not only are the chests hard to open (need like 85%-99% but don't destroy it to open), Scoppio is also going around trying to destroy them too. The boss itself is hard while you're looking for items, but once that's done and you don't have to worry about items anymore, the boss turns to midly difficult.