The Infinity War Secret Character IS NOT,,,,

A lot of people, but I wanted to run down some popular guesses and which ones make sense, and which don't.  I'll do this in the order of what I consider at this point to be the most likely.

1.  TV Cameos - I find this to be the easiest to pull off with little effort.  A quick montage of "everyday people" as Thanos snaps his fingers, flashing around to truly random people as we catch glimpses of Jessica and Luke, Daredevil, or Robbie Reyes.  It's quick and easy and needs no set up or explanation.  It also doesn't confuse viewers who don't know who they are.  To them it would just be people.

2.  Nova - Everything is in place for this to happen.  Xandar could easily be destroyed early in the film for the power gem setting up the stakes of planet destruction as Thanos' forces move toward Earth.  Nova could easily be born out of this event without skipping a beat.

3.  Original Captain Marvel - Not Carol Danvers, but the champion of the Kree.  What better time to use such a classic character who perhaps sees Xandar or another place destroyed by Thanos and is compelled to intervene.  The Kree have already been established, and this could also lead to Carol attaining her powers through some sacrifice he makes, which makes for a solid arc and reason for this to actually happen.

4.  Moondragon - Stay with me here.  Thanos has had 2 daughters that we know of, and we know that Drax wants to kill Thanos.  Would anything be more epic than giving Thanos a badass sidekick who Drax realizes is his daughter that is still alive, having been taken from him and abused?

5. She-Hulk - I was against this at first. I couldn't see them wasting time setting up why Bruce would give her a blood transfusion, because there is no other way to make that character, BUT, then I realized it could be a long plot done over the course of the movie.  She helps the Avengers with some sort of legal issues and gets majorly hurt, Bruce returns and has no choice by the end of the film.  I still don't know if I see the point in doing this, but it could be done with a lot of class, so I have to say it's possible.

6. Pip The Troll - I have to say, I didn't like this one at first, because mostly I don't know how they introduce him as someone worthy to protect the gems as part of a version of the Infinity Watch, and I don't see any other reason to bring him in. But it is possible.

7. Silver Surfer - YES, I know he's with Fox, and therein lies the most massive surprise possible.  No further explanation for why he'd be awesome is needed. Still, I'm not putting money on it.

8. Wonder Man - Now this one is interesting, but not as surprising, so I don't think it's too likely.  We know they wanted to mention him in GOTG2 though, so I guess I have to say it's possible.

9. Sentry - It's possible, but I don't see why.  Nova or Mar-Vell could accomplish the same function more organically to the current narrative, so I don't

10. Red Hulk - I heard this one.  Actually, I kind of like it.  I don't know exactly how you know you (in case it's a spoiler) goes on Rulk on us, but it does kind of feel like that character was placed in the MCU for a reason, maybe.  On the other hand, is it silly?  It might be silly.  I guess we'll see. see any need to try to explain the convoluted back story of Sentry.

11. Red Skull - Yes, he is floating around in space somewhere, but this guy is more suited to return in a Captain America film.  I don't see him being some secret henchman of Thanos.  Just for fun?  Thanos is going to be dealing with Death/Hela, his warriors, probably Nebula, etc.  Red Skull seems so out of place here.

12.  The Symbiote - I would so love for Parking to be on some alien ship in space and find a black ball of goo, and I also don't want the new Venom film to be totally disconnected.  However I believe them when they say it is, which makes Peter finding a ball of goo somewhat pointless, but hey, maybe it's just "not connected", wink wink.

13. Namor - There's just no reason for this.  Why introduce a reclusive fish guy into a universe wide cosmic battle?  What's he going to do?  Join the Illuminati?  Why?  I don't see how he influences this story at all.  I really don't.

14. Modok - I don't see it.  While I think it's possible for the film to start out with a minor villain, much like they used Batroc In TWS or Crossbones in CW, I can't imagine using Modok for that purpose, and don't see why the film needs any more villains than it already has.  There's no point to this as far as I can tell.

15. Warlock - He's not going to be in it.  I don't see a reason why they have gone out of their way to deny it, while introducing him in GOTG2, if the only purpose is to try and still surprise us with him.  That just seems a little silly.  Plus we want the current cast to save the universe, so I don't see the point in bringing in Adam anyway.

16. X-Men characters.  NO NO NO NO NO NO NO NO NO.  It's not going to be Beast, and it sure as shit isn't going to be Hugh Jackman.  They aren't going to give some lazy multi-verse explanation for this, and they aren't going to open up a can of worms as to where the hell the rest of the X-Men are.  It doesn't match anything they've done in the MCU so far, so the final films aren't going to suddenly start throwing shit like this at the wall.  I'll bet anybody who thinks Beast or Wolverine is going to show up $1000 right now, and lay you 2-1 odds.  Zero chance this happens.