The whole Antican/Selay thing was strange. Not in and of itself, but the fact that normally, when visiting dignitaries appear on the ship, the episode revolves around them to some extent. The crew seemed to pay less attention to them than they did to Ralph Offenhouse and his bunch. That's saying something!
You'd think, at least one of the Anticans or Selay could have been posessed by the energy cloud-thing, if only to justify their presence in the story. We didn't know them, but their characterization from the word go was one of mutual hostility. They both came across as sarcastic, at best (actually, that's an interesting twist on a hunter species behavior, not simply aggressiveness or hunter/pray "simplicity").
But that said, how good at hunting are they, to accidentally snare Riker ("Sorry. Wrong species.")? Why would they be lying at wait in the corridors, and why should they expect the other delegates to be wandering around for? Where would one hide in those corridors? And why was Riker walking around in that specific part of the ship? You would think each party would have assigned to it it's own security men, in order to protect each from the other. Proto-O'Brian was all we saw.
Also, Picard seemed to exist in tandem with the energy creature to some extent. He even told the bridge crew that he had officially tendered his resignation from Starfleet. Why would the entity bother with that? It wouldn't, so it must have been Picard's doing. So after Picard is rescued in the end, shouldn't he still be resigned from Starfleet? It had to have been his own doing.