At the start of Chapter 2, when you reach the area where you are on the roof with the donut to your left, you must wait until the group of people by the pit of dead bodies burning breaks up. After a couple seconds, one of the Cell Soldiers will walk under the donut and you have to knock it off with a melee attack.
With Air Stomp you can jump off any building and survive as long as you activate it. For instance, in Dead Man Walking, you can jump off the first building and do an Air Stomp and survive without any loss of health.
During the first level you have the ability to flank some CELL soldiers by entering a small sewer after the subway. There are some electrical wires hanging above your head that say "Caution 1.21 Gigawatts." This is a reference the the movie trilogy Back to the Future where the time machine, made from a DeLorean, needs 1.21 gigawatts of electricity to travel through time. The correct pronunciation is "gigawatts," however, they say "jigawatts" in the movie. Apparently a scientist the movie team hired said it this way.
On the"Dead Man Walking" level, after achieving the "Locate the Nanosuit Deep Scan Cradle: Locate Gould" objective, there will be an elevator at the end of the level. Take the elevator down as instructed. When the elevator door opens, follow the hallway. After the first right turn notice the security camera next to some servers. Jump over the red rope and get close to the switch on the right. Hold [Action] and a red light will appear. Return to the elevator that you used, and jump over the red rope to reach a second elevator. The switch will now be lit. Hold [Action] again, as instructed. The elevator doors will open, showing a C.E.L.L. dance party.
During multiplayer, you may see the "Deflection" suit upgrade on screen. This is not a normal suit module upgrade' deflection is pretty much a deathstreak reward, earned after five consecutive deaths. Deflection can normally be found in the Campaign mode as a suit upgrade. The description in the campaign is: "Provides increased protection from enemy fire by deflecting bullets." The deflection upgrade will be gone after you earn a kill.
In the Campaign chapter Dark Heart, there will be a moment where the suit tells you to do a Tactical Assesment. One of these will say Avoid, which is because there is a very deep sink hole. If you can Grab a Ceph and throw it into the hole, you unlock the achievement.