03-16-2018, 11:37 PM
I would require some kind of Perception check for the NPC to be able to identify the square. The "manifestation" that a psychic spell creates is undefined, as is the interaction with Invisibility. But the intent seems clear to me that they want Psychic casting to be just as noticeable as normal casting. As a result, I would use the same mechanics requiring Perception that I have seen used many times before Psychics existed. Generally a DC 20 +1 per 10 feet away for noticing an invisible creature that isn't stealthing. As a GM that's what I would expect the PC's to have to do in order to pinpoint the location of an invisible NPC spellcaster, and it seems that should be the same ruling in reverse (regardless of Psychic or not). I might make it an easier DC by saying magic is particularly noticeable, but that seems like jerk move to me.
And of course, as you mentioned, you'd still apply the normal 50% miss chance as well.
Assuming you are in a 7-11 (minimum 8th level for a psychic to cast Greater Invis) I would argue that it would be hard for a PC to solo an encounter just using magic missile wands protected only by a rounds per level spell. Your NPC could potentially use the terrain to his advantage to narrow down the places the invisible PC could effect him from, but in general I'd just target someone else in the party, and let them suffer from their fellow party member's selfishness of going Invisible.
And of course, as you mentioned, you'd still apply the normal 50% miss chance as well.
Assuming you are in a 7-11 (minimum 8th level for a psychic to cast Greater Invis) I would argue that it would be hard for a PC to solo an encounter just using magic missile wands protected only by a rounds per level spell. Your NPC could potentially use the terrain to his advantage to narrow down the places the invisible PC could effect him from, but in general I'd just target someone else in the party, and let them suffer from their fellow party member's selfishness of going Invisible.