Scrap the above. I think it is Spock as Kollos/Kollos.
1) The entire bridge witness Spock as Kollos pilot the ship back to Fed space. They also witness the failure to grab the shield, instead Spock decisively enters the cubicle (only to go mad).
2) Why did Kollos (an alien who in his true form doesn't speak or read) suddenly go all Shakespearian?
3) His theatrics and Shakespearian romanticism lead him to forget to put the shield back on.
4) Kollos literally 'blinds' people into madness. His 'ugly' appearance causes the chaos that ensues. The solution is a joining with Spock to navigate the ship, thus blinding the crew to his real appearance. The irony being a mad man got them into this through seeing the Medusan, and it is the very same entity that must help the crew get home.
5) Speaks for itself.
6) We know very early on, the Medusans' extraordinary navigational skills. The sight of the Medusan caused the trouble for the ship, but it is precisely the same being that saves them. Also, the madness of Marvick causes him to pilot the Enterprise over extraordinary distances, in the first sequence. The second sequence, piloted by Kollos, appears to be exactly the same navigational action.
7) 4) Miranda is blind, and blinded to the reality of what must be done.
5) Kollos is 'colourful' and 'iridescent' not 'transparent'.
6) Everyone - I. E us the viewers, see the external sequence of events going to and from the other galaxy. (Those inside the ship don't.)
How's that?
[flashingpsychedeliclightsscreamingmadness]
