...do you have any examples of a modded app that's semi popular to use? I'm just kinda lost on what we're talking about here.

Let's say that you install a modded version of any app on HappyMod. Since the app files are basically compromised you never know what the modder has put in the app. Usually you don't notice trojans, until the police comes to your house after a few months because somebody opened a restaurant in Spain with your credentials (which got shut down due to tax fraud and other bad things) (it actually happened)