such as Alexa's shadowy passenger
I've considered this and since the parasite/symbiot that took residence in Alex when the meteor crashed, turning them into Alexa, might be immune to Schro's powers since it is an extra terrestrial being. The fact that Schro could see through Alexa's eyes might simply be because the parasite allowed him to, as it seemed (at the time) harmless to allow him access.
In the end this could mean that the only one who can truly defeat Schro would be Alexa, or rather her parasite in full shadow form.
I have also contemplated a character with psionic powers (something along the lines of
Phoenix who so far is completely overwhelmed by her new powers and thus has not yet surfaced, much like Marko but for different reasons. She too would be immune to Schro due to the ability to shield her mind from his invasion, maybe even block his powers completely.
However let us first conclude this first "episode".
I am thinking either that Cardio and Cheshire collaborate to somehow incapacitate Blair. (If Cardio wants something heavy to drop on him I am sure there is a tractor or some such vehicle of considerable weight on the Bailey's farm.
Another outcome that I somehow favour more is that Erin resolves the issue in a more diplomatic manner now that it seems Blair has at least heard her explanation for what it was, an order to stand down. Maybe the commissioner had ulteriour motives to not allow Erin to interfere with the Bailey's. (Maybe they grow something illegal hidden among the corn, or one of their barns could be used as a warehouse for drugs or something like that.)
This of course does not mean that Blair will automatically forgive her for not keeping her promise to them but they might perhaps let her go so she can go after the real villain.