If you are just short of an upgrade (e.g. you have 90k EXP and you need 100k), you can earn the amount you need, purchase an upgrade with EXP, and kill yourself and return to a checkpoint and you'll have both the upgrade and the 90k you had at that checkpoint.
Unlockable: Body Surf
To unlock a new ability called "Body Surf," navigate to the Cheats menu (under "Extras" in the Main Menu) and enter this code: RIGHT, RIGHT, LEFT, DOWN, UP, UP, UP, DOWN
Submitted by ProtoMan
Unlockable: New Game +
Once you beat Story Mode, you'll be able to play through it again with all of your powers and upgrades.
Submitted by ProtoMan
Unlockable: Hard Mode
Beat the game on Normal to unlock Hard Mode.
Earning a Gold in every event unlocks Platinum Events, which are more difficult.
Unlockable: Secret Story Event
Complete all Scientist Consume events to reveal Karen Parker's location after her disappearance.
Confirmed by Shampt
Submitted by Mat the Cook
Hint: Easy Thermobaric Tank
First you must unlock the Kill Event called "Rolling Thunder," which appears between the East Village and the Lower East Side (one block from the East coast). Right next to the Event is a Thermobaric Tank. Jumping into it will activate the Event, but you can back out of it before the Event begins. Do this correctly and you'll have a free tank. Note: If you exit the tank it or use it to destroy a Hive or Base it will vanish. You can grab it again at the Event point.
Submitted by Reurbo
Hint: Unlimited EP Exploit
On mission 22/31, where you get the first cell phone cut scene, you'll be asked to jack a Black ops helicopter. Once you have the helicopter, you are prompted to pick up a few Black Ops guys and then destroy a Hive. Do not destroy the Hive!
You now have a helicopter with unlimited missiles, no time limit, and as long as you don't destroy the Hive, you can blow up anything else without it kicking off the alert meter. This also allows you to get out of the helicopter without it ending the mission (useful for collect Memory Strands).
The easiest way to get EP in this is to switch to your Infected Vision and fly around blowing up infected water towers. You can save your game in the middle of this mission if you need a break and do the same thing. You can max out your skills and then some using this exploit.
Submitted by TRKghost
Hint: Smooth Landing Speed Boost
After jumping, avoid using both of your dashes while airborne and save one to use just before landing. If timed correctly, you should hit the ground at near full speed, which is very useful when attempting to evade the military or during a timed activity. Note: This doesn't work for the highest of drops.
Submitted by DarthDelirium
Hint: Mind the Crows
Infected water towers are always circled by squawking crows. This makes it easier to track them down
Submitted by ragemoonheart
Hint: Collectible Vision
It's sometimes difficult to spot Landmark and Hint Collectibles. Switch on your Infected Vision (or Thermal Vision) to help discern them.
Additions by Eternis
Submitted by Iron-Death
Hint: Easy "Misconception" Achievement and EP
The "Misconception" Achievement requires you to destroy 25 infected water towers before they hatch. Do this after you get your powers back -- when Ragland helps you -- as there seem to be more of them in abundance. Lock on to one and run up the corresponding building, jump to the roof and use the flying kick attack, causing more than half of the life bar to be depleted. Upon landing, follow up quickly with a combo. To make it a little faster, use the "claws" powers.
Later in the game this becomes even easier. Just hijack a helicopter, fly over infected areas and keep tapping the target button until you target a water tower (or helicopter or Hive) and fire away.
The "Friendly Fire" and "Projectiles" Kill Events as both have helicopters sitting next to the Event markers, so grab those and exit the event for a free 'copter.
Additions by ctpeters0 and Reurbo
Submitted by AjaxRoxx
Hint: Final Boss Strategy
After the cut scene ends, quickly switch to Armor and Blade (Infected Vision also helps). Stay away from your opponent until he starts to jump after you. When he lands, hit him with the Air Blade Slash. Get in a couple of good hits and he should be stunned. Grab him and repeatedly hit the PUNCH button. If he knocks you down to critical, use a Devastator move to stun him.
Submitted by xzxRebellionxzx
Hint: Orb Collecting XP Rewards
You'll receive XP for each Orb you pick up. That value is based on how many Orbs you've collected. These values are given below in addition to the one-time bonuses you get for reaching certain Orb collection milestones.
1 - 2,600 each
10 - 5,000 each (+10,000 bonus)
25 - 9,750 each (+25,000 bonus)
100 - 15,000 each (+50,000 bonus)
125 - 17, 250 each (+60,000 bonus)
150 - 20,000 each (+70,000 bonus)
1 - 5,000 Each
10 - 7,500 each (+10,000 Bonus)
15 - 12,500 each (+25,000 Bonus)
35 - 15,000 each (+50,000 Bonus)
Submitted by IGN Guides
Hint: Flourish Move
Once you purchase a power in Prototype and have it set as a shortcut move, you can then hold down the shortcut button to do a flourish move with the power. It's a unique, if useless, animation.