Well, I'm thinking that Freddy would sort of yell at Roy ALL THE TIME. Just like, "Don't you freaking DARE do something stupid! I swear I will collect your freaking imps and shove them through your digestive system backwards with nothing but pure Concussive Force shouts!" At the same time, he'd keep annoying him to see a therapist.

"Believe it or not, Puck, you neverending douchecanoe, your mental stability is KINDA important! You don't even have to start taking meds or anything! God knows I don't! So, get your ass to a good freaking therapist, work with him, and get freaking DIAGNOSED because there is literally no way you don't have some sort of serious mental issue!"

And, of course, Freddy would do so because he loves his friend and wants him to be happy.

I just realized that Freddy aspires to be the team mom. A very angry, yell-y, team mom.

Edit: Out of curiosity, how would everyone's characters react to Freddy's raving, loving, protective, endless douchery?