Plutonium

@Eternal_Blue87 I would say if you downloaded a mod that changes textures/audio that it would only apply to you. But I've never played a mod with someone who doesn't own it, if the mod changes gameplay via GSC files and .lua data (for example, scripts that make the player able to view with no fog, or pull out a tactical knife that wasn't originally in the game). I've never seen that in action before and I just assume either the other person is halted by the game to download it before joining, or the game would just crash later on. If it's just something that's only for cosmetic change, like textures/audio, you should be pretty fine.