I did this with Captain Falcon and Ganondorf, getting around 3,200 feet with CF and around 5,400 feet with Ganondorf. I jump, drop the homerun bat at the peak of my jump with Z, do a meteor smash(down + A in mid-air), then L-cancel. After that, I jump, then catch the homerun bat with Z, and drop it right after I catch it with Z. Finally, I use a meteor smash and then repeat the whole strategy again. At the end, I do a Falcon Punch or Warlock Punch, depending on the character. The sandbag should have around 260% damage after you're done hitting it with Ganondorf(not sure about Captain Falcon). Yes, I already know this is ALMOST the world record strategy.