Here's the way I understand the mini skulls: A mini skull represents which of the 5 randomly loaded chapters/scenes for that movie is set to be played if you hit the start chapter area. If, for example, you have hit the left orbit shot (yellow skull) to qualify playing a COTBP movie chapter/scene then a mini skull will appear telling you which of the 5 chapters/scenes for COTBP you will be playing when you hit start chapter. If you hit the left orbit/yellow skull shot again before hitting start chapter, then the mini skull switches to one of the other 4 chapters/scenes to show that chapter will now be the one you play when you hit start chapter. I think that's how it works but I could be wrong.

A skull hold carries the value of a skull shot to the next ball. Ordinarily, for each ball the skull shots start at a certain point value (I think 1,000 points) and then various things can increase the value of a skull shot (mystery award, hitting the skull shot, etc.). So for example if you got a mystery award to increase the value of the purple skull by 250, the value of that skull shot would be increased to 1,250 for the next time you hit that shot. If your ball drains without having a skull hold, the purple shot will reset to its starting 1,000 value for the next ball. However, if you have a skull hold for purple then the starting value of the purple shot for the next ball will be 1,250 carried over from the previous ball.

I think the max skull shot value you can get up to is 10,000 per shot and then it stops increasing.

Dead Men Tell No Tales (Movie 5) Multiball. The arrow is purple. When other multi balls are going at the same time and are also lighting the arrows (green for Dead Man's Chest MB or yellow for Tortuga MB) then the arrows alternate flashing the colors for each different MB, so it can be difficult to spot. After you hit it the path to the Devil's Triangle shot lights up white for a super jackpot.