In our Story the grogs and the magus met a fearie (smoothface from antagonists). He took the face of a grog and infiltrated the group just to reveal his true nature and frighten his victims later. It was a great session, but I, as a stroryguide, wasn't quite sure about, if it is possible to recognise supernatural creatures (especially fearies) with InVim-Spells (no such guidline) or like in this case InCo-effect for this smoothface (might 10).
I ruled that it isn't possible. Later in game, when one magus didn't penetrate the fearies magic resistence with "frosty breath of spoken lie", he was sure that it must have been a supernatural entity (or being protected by another parma magica, relic,..). I also read in ROP:F that you could recognise a fearie using a pretense, if you have an ability 6+. And maybe with fearie lore you could destinguish a fearie from a human being. But do I overlook something? Any tips or advise?
Thank you, Jason. I couldn't figure it out during gameplay. So to detect a fearie of might 10 it would be a spell like this:
InVi: 30 - Smell the fearie's aroma
Base 5 (any magnitude) +1 Conc, +2 Smell +1 for fearie +1 determine form
After casting you can detect any supernatural creature of the fearie realm and its underlying form by scent of it.
If it would be of higher might, it would be easier. Therefore a might 30 creature would only need InVi 20 (Base 3)
So you'd need a casting total + penetration bonus of 40 + some points extra because of the surrounding fearie aura adding to the creature's (resistence) to detect a 10-might-fearie. This makes it pretty tough for a magus just out of gauntlet. Altough a level 20 version to smell only the "supernaturality" of creatures, seems quite possible.