Is it possible to simulation some sort of picture fade-in effect?
Currently I flash the screen and then create the image with partial opacity, then move picture to set the opacity to 0. Then I erase the picture.
But what if I don't want to flash the screen, but instead want the picture to smoothly fade in?

EDIT: lol nvm, I just had to create it with 0 opacity and then increase it later.

I would also like a similar effect when using a skill in battle. Basically, a picture would flash in, and then fade out before damage/effect is dealt.
The easiest way would probably be to create an animation and assign it to a particular skill, but perhaps there are other methods (that don't involve too much scripting, if any at all)

Unfortunately, I can't think of any solutions to your second problem that don't involve scripting. Or, rather, there are other solutions but they'd be even more difficult without scripting. This is just for one skill in particular?

Can be expanded to many skills (flexible design), but I don't see anything beyond just one for now.
Are there any script systems that are already in place for this sort of thing? I could look into those.