Call of Duty: Modern Warfare 2/Perk 2

There are five perks available to use in the Perk 2 slot. For each of these perks, a "pro" version of the perk can be unlocked by completing its specific challenge. The upgraded perk's effects are combined with the original perk's effects, which means perks can give two effects from one slot.

Stopping Power is very useful for snipers as it usually means bullets are 1-shot kills. It is not as useful with people who move around more as normally if you shoot first you win. The Pro perk isn't very useful as you usually have people with Launchers to destroy the aircraft. Overall, it is a good Perk at the start of the game as it's useful in most situations, but as you gain new Perks, there is usually a better option.

Lightweight allows you to sprint faster, this can be very useful if combined with Marathon as it allows you to sprint for an infinite period of time. This can be used to get easier knife or riot shield kills or alternately play as a flag runner in Capture the Flag. The Pro version of this perk is fairly useful as it allows you to start shooting faster. Levelling up this perk is easiest on game modes where you do a lot of running (Capture the Flag, Search and Destroy or Sabotage). You could also run against a wall to do the challenges.

Hardline allows you to get killstreaks one kill earlier. This can help with the Killstreak and Prestige Challenges. It is more useful for people who have a low Kill:Death Ratio as it means they may get another killstreak before they die. Hardline Pro means you need one less death to use a deathstreak which can also be useful if you have a low Kill:Death Ratio. This means it is more useful on people who run around.

Cold Blooded is very useful as it allows you to run outside when enemy killstreaks are around and they will not directly target you. You can be killed if an ally is near you. For the Chopper Gunner and AC-130 streaks, you can be seen, but do not have a red rectangle around you, so you are much less likely to be spotted. If you have this perk, it is a good idea to carry a Launcher as a secondary weapon to shoot down the enemy killstreak rewards, this will get you closer to unlocking the Pro challenge and can help your team to win. This Perk can also be useful to stealthy characters as it makes you invisible to UAV, you will still show up if you shoot without a silencer though. The Pro perk can also be useful as your name will not appear and cross-hairs will not go red when you are near enemies, this means you maybe able to kill a few enemies before they realise that you are not on their side.

Danger Close can be useful with many explosives as it makes them even more deadly, Claymores are much more likely to kill and grenade launchers are made even more powerful. The Pro version of this perk will help you as your killstreak rewards deal more damage. To help get the challenge, equip the Thumper, an Assault Rifle with a Grenade Launcher and a Frag Grenade/Semetx for the most chances to get kills. Scavenger or One Man Army will help restock ammunition.