Design in correct mobile dimensions
Remove CN logo in the second postcard
Include names of characters who say the quote
The text in first postcard could benefit from bring two lines. It's also too cloase to the left edge.
This is a monor thing but there's a weird black border around the first two.
Text becomes a little too small in the last postcard. But I think this will get resolved once you start working in the correct mobile dimension.
For the fourth postcard, the text is too close to the left edge.
For the fifth, the image of the unicorn is too close to the top edge. Maybe include more of the sky to serve as the top margin.
Same with the last one.
The first four does a good job of image cropping when transitioning to desktop and mobile.