Normal vs fighting not good!
Focus blast to the face not good!
Lv 100 lucario not good!
yeah u do that!
alright then lets do this. if focus blast hits under normal circumstances rattata would be dead on impact, BUT, this rattata happens to be carrying a little item called a Focus Sash that allows it to survive what would normally be a 1hko (abeit with 1hp, )
I then use a little move called endeavor, which when used will bring your opponents pokemon to the same amount of remaining HP as the user.
thus both pokemon are down to 1hp, Your move