Grimrock

Hello all,
I'm at the place "outside" where There is : at one side and And there is a monster here I cannot kill ... I can be hit by ne weapon in my possession ...
What's the hell ?
Someone have any clue please ?

I think this has been answered multiple times already on this forum, but anyway, the Air Elemental (that green thingy you can't damage) can only be hurt by using the Dispel spell or the Ethereal Dagger (pretty nasty mob if you ask me, but easy to kill if you have the means).
Hope this helps.