Brace in midair
When the ground starts to shake, you can keep running. When it shows you stumble and fall, if you are quick enough, you can press "Brace", and get in the brace position from midair without taking any damage. Then, just get up and keep moving.
Invincibility
To get invincibility: press up, down, right, left, right, left, right.
Secret room in water system
Go to Karen's house. Goto the water system area after her house and past the subway. In under 2 and a half hours (total game play time). The entrance to the control room will be unlocked (usualy it'll be closed). Inside you'll find the "CC Compass" and other stuff.
Brace in midair...