My party's going to be encountering an Elder Oblex that's gained more sentience than usual. The party has a mirror of Scrying (cast once per day without components/slots). They're wanting to use said mirror to spy on the Oblex, get an idea where exactly it is, plan an ambush for it.
Elder Oblex has blindsight. Assuming the Oblex fails the save to resist the Scrying spell, would it notice the sensor created by the spell? The sensor is invisible, which would be ignored by the blindsight, but I'm not sure if the sensor does any other kind of sensory effect that could be detectable by blindsight.
The exact wording of Scrying is:
On a failed save, the spell creates an invisible sensor within 10 feet of the target. You can see and hear through the sensor as if you were there. The sensor moves with the target, remaining within 10 feet of it for the duration. A creature that can see invisible objects sees the sensor as a luminous orb about the size of your fist.