Sometimes when I'm using a mod offline like a parkour mod, I want to see the result. But there are times where my tori looks like they are running in the air. Help would be appreciated.

Do you have the replay mod in your mods folder?
If you do, does it have the same path as listed in replay file? Mod path replay would be looking for is listed in NEWGAME line if you open it with any text editor.

I'm not sure what you're on about. But would it be better if I showed you a video of the problem?

Yes, please do

Here's the video: https://youtu.be/zepe8TRtWI4

Alright, you're missing the mod file. Make sure it is located in your mod folder (Toribash/data/mod) - file name should be the same as mod name that replay file is looking for.