Yeah it’s not some big secret at all! It’s just move picture. So I show/set the picture just off screen and then have it move. It’s easier in MZ because you can use quicker placement whereas with MV you have to use pixel coordinates. But just show picture, starting with just a sliver of the image on the edge of screen and then move picture 60 seconds, you can adjust how fast it does it (I did slow start slow end to give it that wave feeling). I used common events so it was easier to do quickly as I went along. I had a MC1 in and MC1 out common events for the images coming and going.
It’s funny, honestly I think bust images are so fiddly they drive me nuts haha. Every time I do them I regret it cuz it’s just! Fiddly! But they add a lot and you can do a lot with them. I think HoneyNutFemios is a good example of doing bust images and movements really effectively. Move picture is also how I did the waves effect at the start of drift away. There’s so much you can do with them. WAY easier with MZ tho. Less math haha.