I had terrible trouble getting minikit #7 and found no helpful answers online so I thought I would post my solution. I honestly thought my game was broken and had all but given up reaching 100% bc of this...This is the mini kit on the wagons that appears behind the wagon you build the ramp on. It is in a silver box that requires an explosives character to open. My problem- it was fully accessible in story when you have no access to explosives... but inaccessible or flat out invisible( as in, the wagon was NOT there) in free play. I tried many things unsuccessfully including replaying, reloading in every imaginable sequence etc. I finally succeeded when I played free play exactly as I play story thinking perhaps I was skipping something & discovered the problem was that I was not shooting the target on the wagon a few back which makes a ramp roll down. This action seems to trigger the wagon's appearance... you will notice it dash by in the background after shooting the target. I was skipping it as free play allows a double jump character and it was unnecessary. Hope this helps someone:) Don't know if it is a common problem.