Randy in Stab
I was very thankful to finally see "new" footage from the original Stab movie, but I was disappointed that Randy wasn't played by a young 'it' actor of the time. They already were using de-aging on Skeet Ulrich (to... well, SOME effect), so why not for one more quick appearance?
Would have been a little added fun to see someone recognizable (as was the point in Stab castings from Scream 2). My mind went to Ethan Embry because of Can't Hardly Wait. Or also Breckin Meyer. He's barely aged anyway so the de-aging process would work just fine!