I’m 99% sure that this was a rumor spread because of the speculation that Phantom Wraith was the Ajax Monster. There was a lot of misinformation spread around since the End of Evolve Q&A (understandably so given how hectic and sudden 2K’s contract ending was), and I’ve done my best to keep it all straight. I’ve fact checked my notes extensively, and I can’t find any official source that takes the story in that direction (though if I missed it, please direct me there! I am always open to new info).
To the extent of things I have for certain, Phantom Wraith is the one being vivisected in the wraith trap. It evolves to an insane power level through months of what is essentially torture and escapes containment. The Crew is sent to kill it, however it turns the hunt around and kills most of the Crew - Caira for sure dies here, and possibly Griffin. We don’t explicitly know who dies, but we know that Abe, Cabot, Maggie, Hyde, Lazarus, Bucket, Sunny, EMET, Parnell, and possibly Jack make it out alive. It is unclear if this is the only phantom wraith, or if more spawn over time.
As for main antagonists, Kala is the biggest baddie outside of Patterson himself. Patterson is the reason the Monsters attack in the first place, and Kala is the one that ends up unwillingly hyper-accelerating the proliferation of the monsters across the universe. As far as I know, Kala is the only completely unique monster.
That being said, I’ve seen the rough draft (Shika works insanely fast - no idea how she does that, but holy geez it is impressive) and it looks BEYOND villainous. We’re discussing adjustments now before things get polished (though if you ask me it already looks way more detailed than a sketch. Artists blow my mind).