Presumably, the wizard casting Finite Incantatem must be more powerful, possibly significantly more powerful, than the wizard casting the original spell, or Finite Incantatem would be taught as a defensive spell and would be much more widely used in dueling
The word Petrificus Totalus is an alteration of “totally petrify”.
The complete Body-Bind annoyance, this spell causes the victim’s body to go entirely inflexible, with their arms stuck by their side and their legs snapped jointly. The single object that they can still move about at the same time as in the pressure of the magic is their eyes. This annoyance has been used on various occasions during the series. It was first seen when Hermione to some extent regretfully cast it on Neville at the end of their first year, when Neville was trying to discontinue the trio going to recover the Philosopher’s Stone. Neville seemed none the inferior for his suffering afterward, and was much admired when Dumbledore gave him 10 House Points for standing up to them, which gained Gryffindor the House Cup