Shadow, you likely have an older version of the game. The initial release had a bug in it where you could use the rock when Vaektor wasn't in the screen. That has been fixed in the version now downloadable (which it sounds like Rutitah has, since he can't use it).
Shadow and Rutitah, to defeat the elf, you're on the right track, using a magic spell. You'll need to maybe try another one. Feel free to experiment. Each spell has a different effect. Maybe one will work where another will not.
Let me clarify to lessen any frustration. You'll need to use a magic spell:
For a total and complete spoiler of what to do :