I'm looking to find out how to determine the might level of a magical beastie. Now one way to do it would be to cast might based spells at it in increasing increments until one of them works (or the penetration fails to get through). But is there a guideline (I'm guessing InVi) that allows you to determine the might level of a magical creature?
I had once a player in a game I ran inscribe a series of wards of gradually increasing level in a hallway. He then forced his target down the hallway and observed where it stopped.
For this to work you need to be able to see your subject and force it down a prepared hallway. It wouldn't work for all situations.
Realms of Power:Magic p111 is your friend, the box there includes a bunch of Intellego spells that need to penetrate.
I think then, that given those spell guidelines, or using wards some kind of process would be required, rather than a single spell. I like the idea of a corridor that sorts beasties based on how far they can go down it. I might also try concentric warding circles.
I would think that InVi could manage, the trick is needing to penetrate while using spell guidelines based on detecting things with a magnitude greater than x... magnitude 4 allows you to discern the magnitude of vis and detect spells over 3rd magnitude, base 10 allows you to detect the gift, and base 1 allows you to detect the presence of vis. I don't think extrapolating to a base 20 to allow detecting magic might would be too far of a stretch...
The creature in question needs to survive right?
A Perdo Vim effect with non momentary duration combined with a rough guess and a ward spell would give you a really cruel way to approximate it.
Or a touch/sight spell cast with normal voice/gestures and then varying them to crudely reduce the casting total?
If ypu know the form I think you can use the guidelines on RoP:M pg 111