Shadow Conjuration + Invisible Stalkers from summon monster 6.

[killem2]

So I have a fight coming up for my players that involves something summoning 9 Invisible Stalkers but because of Shadow Conjuration. (Via Shades spell like ability)

It states in the spell however:
Shadow conjurations are only one-fifth (20%) as strong as the real things, though creatures who believe the shadow conjurations to be real are affected by them at full strength. Any creature that interacts with the spell can make a Will save to recognize its true nature.

Is this just assumed to happen when they get smacked by the Invisible Stalker? How can they believe what they can't see?

But then there is this:

A shadow creature has one-fifth the hit points of a normal creature of its kind (regardless of whether it's recognized as shadowy).

Again, they are invisible. How do you rule this?

[eggynack]

Not all disbelief necessarily has to come in the form of sight. You can feel or hear that something is off instead. And getting hit definitely counts as interaction, so it would trigger the will save. Also not sure at all what being invisible has to do with having fewer HP. That one seems completely unrelated. Honestly, this doesn't even seem to be a thing that needs ruling. The spell says that certain things happen, and there's no exception for invisible creatures.