The See Invisibility spell is a well-balance and popular spell. While it can also view ethereal creatures/objects due to the Ethereal plane being coterminous with the Material Plane, it cannot view creatures/objects on the other coterminous plane ... the Plane of Shadow.
I'd like to make a higher level version of See Invisibility that can view creatures/objects on both the Ethereral and Plane of Shadow. I'm thinking it would be as simple as boosting it up a level to Bard 4 & Sorc/Wiz 3. Perhaps calling it Greater See Invisibility
If I was to boost the spell up to Bard 4 & Sorc/Wiz 3, would it be unreasonable to also give the revised spell the benefit of allowing for no "random shunting" effects from a caster who is currently running this Greater See Invisibility spell who then casts Shadow Walk?
I'd like to piggyback that bonus effect onto the Greater See Invisibility spell. But boosting it +2 levels from the base See Invisibility spells seems to be too much.
Please advise if you think I need any precise rules additions/modifications to ensure the revised spell (with the Shadow Walk rider) will be stay balanced. Thank you!
The whole point of See Invisibility is to see invisible creatures. The reason it also affects the Ethereal Plane is because ethereal creatures can see into the Material Plane and abuse this to become undetectable. This isn't the case with creatures in the Plane of Shadow. As a result, a spell that lets you see into the Plane of Shadow is essentially letting you scry an area in another plane of existence with no risk of failure. It should be no less than a 4th level wizard spell. If you add more effects, then you need to increase the spell level.
I'm not sure how this spell would work considering that the Plane of Shadow does NOT have a 1:1 mapping with the Material Plane. It's a separate plane of existence.
Thanks for your valuable input, Cyrad. I'm going to have to go back to the drawing board on this spell concept.
Actually I did pretty much what you were suggesting here in my campaign as well. I looked at the "invisibility" effect from LOTR with the One Ring, which was actually more a dimensional shift than true invisibility. I rebuilt invisibility around this concept, and also added the fact that anything which was invisible was also visible to things in the other dimensional space. One had to be careful where such effects would be used. Grave yards, dark temples, etc could be very dangerous places after all.
Yes: I used this mechanic to discourage the use of the spell (it was a low magic campaign setting)