Once you fill all the blue shell soul boxes, the ? blocks will disappear in the giant open pinball area with double tap & whatever other perk is there. There the teleporter will appear in the middle.

Fill all 4 of the blue shell soul boxes and then activate the teleporter, it should say something like "waiting for power" er sum.

Behind the tele there are 2 half walls with arrows pointing towards the tunnel to the finish line, the left one will have a shield part behind it and the behind the right one will have "Waluigi's Wrench" sitting on top of the half wall. Pick that up.

Run back to the power switch at the start and interact with it to "run wire". Once thats done, go back to the tele and you should be able to get to PAP.

Hope this helps :)

Idk about the DS locations but I couldn't find any guides on how to find PAP so heres that. Pack ur weapons and pop off lol