Probably one of the most confusing/aggravating things about the remake is the way you catch ghosts. Unlike the original, you have to "wiggle" in one direction. You can tell if its working if the HP is going down by extremely fast. If that is happening, whatever you are doing in that moment, you basically just have to keep that movement up. One problem you might encounter is that the ghosts with stronger pulls (i.e Biff Atlas and Slim Bankshot) will cause Luigi to topple over. If you ever see Luigi bending over while catching you should stop wiggling and only pull in one solid direction. Once Luigi props himself up again, you can start wiggling again. You should typically just use a small wiggle.

For Boos, I have found that moving around in a circle works very well. While R pumping does exist, it really only helps when you have ice.