Thanks for the reply! Actually, the issue is regarding the specification of the classes in the script configuration... I'm having some difficulty on how should I do it to move a picture and change its opacity.I haven't been done anything RM-related in a while, but the default :linear movement should behave like the normal Picture Move command of Ace in a sense that it moves gradually. Are there other script commands related to the picture, that could be interfering with mine or (unlikely) is the game having general FPS issues?
I have done both fading (opacity) and movement (x, y) of pictures using this script in the past and it worked fine for me.
picture = $game_map.screen.pictures[<picture_id>]