Insanity is currently in the prosses of being rebooted so I can’t say much. Horror on the other hand is a lot more complex, he isn’t insane per se but is highly sadistic and internally has a lot of self hatred because of what he has done (almost killing undyne and alphys, killing humans, destroying the core, ect), the man hadent eaten in 7 whole years until Aliza showed up. There’s actually a lot more if you were to read the comic