Cain knew that the humanoid forms of the creatures he had seen, particularly the leader of the beasts, was not their real forms.
Instead, they were simply renditions that allowed them to better expend their energy.
In their humanoid forms, they didn't need to expend as much energy as they would in their normal forms.
However, in doing so, they were also unable to output as much energy as they were naturally able to, should they retain the humanoid forms, leaving them at somewhat of a disadvantage.
He had gotten to see Roc's true form,.but he had not seen Ambrosia's true form.
And to say he was shocked or surprised, would be doing his state of mind a disservice.
Mesmerized? Appalled? Frightened? Enchanted?
Maybe it was all of that and then some, or none at all!
Either way, he really couldn't understand what was before him.
With the largest pair of wings he had ever seen, Ambrosia had become an enormous creature who's wings had enveloped the sky.