I'm trying to write a story where the PoV character and the Player character are two separate beings in the same body. The player has possessed the PoV and said PoV is reasonably terrified about the fact that he cant move his own body. But, I found that it's very hard to implement "show don't tell" when the PoV literally can't show anything. The only things he can do is describe what he see's the player doing and talk to the player directly to try and make the player choose the choices he wants them to choose. Essentially what I'm asking is how to liven up this characters' internal monologue.
I think I explained things wrong. The PC and the PoV are literally two different things. This is more like the Pixar movie Soul but instead of the black dude becoming a cat when the soul takes his body he becomes nothing more than a voice that the soul controlling his body can hear. He has no control over his breathing, his blinking, or even his heart rate.
That's kinda what the story game's about. You have control while he doesn't. The whole "I have no mouth but I must scream" thing. The player can choose to either speak back to the PoV and try to make him feel like he has some sort of agency, or ignore him to achieve their own goals and he's trapped watching and unable to do anything about it.
If you're determined to have the narrator have zero control over their physical actions, a stream of consciousnesses approach could work (where you're narrating their thoughts directly rather than separating them with tags like "I thought" or "I felt"). Stream of consciousness is tough to do well, though, since if it's too direct it comes across as telling, and if it's too indirect it just confuses and irritates the reader. In my experience, the trick is to have the narrator make observational comments on physical stimuli rather than describing their thoughts or emotions. Then you use these comments and reactions to "show" their thoughts rather than tell them, as the reader can still use this method to infer emotional state indirectly.
It's tough to give advice for this question, since there's a number of plausible different directions you could approach this from. Knowing more about the narrator's personality might help. A funny or snarky narrator will be easier to do this with, whereas a frightened narrator would be much harder to potray entertainingly.
First, I disagree that "show don't tell" is a maxim that must be followed at all costs in all fiction writing.
Second, if the POV can't show anything you have no story, so consider some ways you can show.
First person is going to give you a very strong voice but with two first person voices it could become quite confusing for the reader.
As far as how the POV can show with no body:
Perhaps the POV does not lose all control at first, but rather slowly as the player gains control. Or the POV is constantly fighting and can occasionally move one extremity to cause violently hilarious situations. The player can also evidently "hear" his voice, right, so the POV can be saying snide things like "If I had control of my left eyebrow, I'd be raising it." Or the player could feel a chill up his spine or sneeze unexpectedly. Or become dizzy. Various mechanics could be used, and you could always consider that the taking over of the POV blends their minds in a way that it is difficult to tell one from the other, both from the player and POV's perspectives.