I spent a few days working on Mermaid Mission Titanic, recently. This game is going to be great! It's mostly finished, too. I'm just waiting for the rest of the artwork to be done, so I can put it in the game.
90% of what I did was adjust character locations. Moving characters around the screen can be hard, as it's totally inconsistent from character to character. If I put the main character in vertical position 1.1, the daughter in vertical position 1.1 and Andreas in vertical position 1.1, they're all in different vertical positions! I had to do a LOT of guess and check to place them in the correct spots.
Ren'py has three pre-defined locations that you can place characters: left, right and center. That works perfectly for all the mermaid characters. It doesn't work for the humans. The vertical alignment is off by .1 (.2 for Andreas). Maybe the humans are too tall? The copy of the game with placeholder art uses those three locations in every scene, so I had to go back and change every one by hand.
About 80% of the way through programming, I realized that, duh, I should have defined my own locations. You know, human left, human right and human center, which are the same as left, right and center, just moved down by .1. That way, I could have used replace to change the character positions in two seconds, instead of taking hours to do it by hand.