1. Challenges
1.1. Be More Objective – 3 Star Challenge #1
1.2. Parkour This – 3 Star Challenge #2
1.3. Escort Duty – 3 Star Challenge #3
1.4. Tower Defense – 3 Star Challenge #4

2. Miscellaneous
2.1. Boom! – Detonate a HE Charge
2.2. I think I know a shortcut – Open a shortcut for your team
2.3. Cut ’em off at the pass – Close an enemy team’s shortcut
2.4. Brinksmanship – Operative Primary Objective within 5 seconds of breaking disguise
2.5. Not so sneaky now, are you? – Reveal an enemy in disguise

King of the world!
There are 4 Challenges in total. You have to complete the first two of each kind before being able to play the 3 Star Challenge. The Challenges do unlock lots of weapons and weapon attachments which is another reason to complete them. As soon as you completed all 3 Star Challenges you will be awarded with a nice Trophy or Achievement.

-Challenge #1 (Be More Objective)-
‘Be more Objective’ is the hardest one. You are playing against a team of AI enemies and have to complete some of the most common primary objectives of different character classes.
This has been played with a newly created middle-weight character, no abilities have been bought and no weapon attachments were used. The key to be successful is speed and knowledge of the map. Wait until enemies are distracted by your team members. Flank them and run straight to your target.

-Challenge #2 (Parkour This)-
‘Parkour This’ is the easiest one. You have to run or jump across numerous light beams. The 3 Star Challenge can actually completed in half of the available time. When you perform some stylish moves (e.g. wall jumps) you will get a speed bonus.

-Challenge #3 (Escort Duty)-
‘Escort Duty’ is pretty easy. This has been played with a newly created medium-weight character and the standard preset of weapons. No weapon attachments were used and no abilities have been bought. The fact, that you are having so much time makes this relatively easy.

-Challenge #4 (Tower Defense)-
‘Tower Defense’ has a medium difficulty. After playing Brink for a couple days you should be able to get this in your first try. When you are still unfamiliar with the AI tactics you might need a couple tries.
In case you are already on Rank 5, you should buy the Gatling Gun Turret ability for the Engineer. Turrets will help you quite a lot during this challenge. They distract enemies and weaken them.
I did it with a low level heavyweight character. Primary Gun: CARB-9 MP (+attachments), Secondary Gun: Kross MP (+attachments), Abilities: Light Turret.

Boom!
Detonate a HE Charge
This can only be done while playing as a Soldier. Probably the best spot is the very beginning of Day 4: Dirty Bomb (Security Campaign). Run straight to the first primary objective and plant the Charge. Now you have to defend the area for 40 seconds. I suggest to play on easy when trying this.

I think I know a shortcut
Open a shortcut for your team
This can easily be done on Day 4: Dirty Bomb (Security Campaign) while playing as an Operative. When the match starts you should run to the shown location as fast as you can. There shouldn’t be any enemies in your way. Wait until the door is completely hacked and the trophy or achievement will pop.

Cut ’em off at the pass
Close an enemy team’s shortcut
There is a good spot in the first What-If mission of the Resistance Campaign. You have to play as an Engineer! After the match starts you should run straight to the shown location. Repair the Side Barricade.

Brinksmanship
Complete an Operative Primary Objective within 5 seconds of breaking disguise
Play a private match against one bot on the Reactor Map. Make sure to set the amount of AI enemies down to a maximum of one. Allow players to switch teams.
As soon as the match starts you should join the resistance team. The AI enemy will automatically switch to the Security Team. Choose an Operative and hack the primary objective. Kill your enemy each time he respawns and keep hacking until you have at least 95% done. Now wait for the enemy to respawn once more, kill him and disguise yourself. From this moment on you have a total of 5 seconds to complete the hack. A short cutscene will start and in case you were fast enough you will get the trophy or achievement. It’s recommended to play on easy.

Not so sneaky now, are you?
Reveal an enemy in disguise
There are two basic ways to get this while playing against AI enemies. Maybe you will get it somewhen by accident when shooting around. When you shoot a disguised enemy he will be revealed as well (can be done with all character classes). I personally found the shown strategy a lot easier. Buy the Homing Beacon ability (requires rank 2) for the operative. Now start a game on a map of your choice. I recommend to set the difficulty down to easy. Kill an enemy and disguise yourself. Now head over to the enemies spawn area and camp there until an enemy operative spawns (check out the icon next to the health bar to see character class). Aim on him to mark him, follow him, hope that he will find a corpse and disguise and finally mark him while he is disguised. Bling, the trophy or achievement should pop. Alternatively, you can boost this in Multiplayer with a friend.