Okay...
Black Hole - Destroy one monster is too strong, scrap it. Destroy one permanent is too weak, Deflag can do it cheaper. SCrap the whole idea.
Increased Gravity: I guess it is alright. I hope the boost doesn't stack, as it would be too strong otherwise.
Terminal Velocity: It is fairly alright. Flying Titan + This may be an instant kill, but you're paying like 10 Gravity, 3 cards and can't be dealing... wait. To the player? Naaaah. Make it damage a target creature instead and it'll be alright, otherwise it sure is overpowered with Titans.