Invisibility?

So what does this do in combat? I cast Improved Invisibility before the start and an enemy spellcaster hits me with a spell before I cast anything. So what it invisibility supposed to do?

Thanks

It's a PvP spell that makes you invisible to other players.

So what does this do in combat? I cast Improved Invisibility before the start and an enemy spellcaster hits me with a spell before I cast anything. So what it invisibility supposed to do?

If there is no one else in your group, all monsters can still see you. Some monsters can see invis even so. The way to solo with invis is to drink a shift potion, cast summon faery queen in round 1, and improved invis in round 2. Then summon more FQs