What are some crazy hard or ridiculously fun co-op games on the PS4?

Me and a friend love co-op games. Like we've been gaming together since we were both on ps3's. playing LBP and resident evil and things like that. We've both just kinda want more. more fun or hard or both. We are currently running through all of resident evil 6 on no hope mode from scratch to give us as much of a challenge as possible. What I wanna know is what do you and your buddy play? what's some uber frustrating online coop craziness that we can dive into?