What I mean by that is if one person is touching a part and another one isn't, the person in the part has less (or more) gravity, while the one that ISN'T touching a part has normal gravity. I KIND OF already know what the script is, but I don't know what kind of script.
For this script, you're going to need to use a regular script, and insert it in the part. You must identify the characters humanoid when they touch it. And by doing that, you change the Humanoids gravity in the script, because that's where it's located. So to answer your question on what kind of script, you need to use a regular script. Comment on my answer if you need any further help.