Where are the Collectibles? Collectibles are placed throughout each level of the single player campaign.
How do I view Collectibles after collecting them? You can’t; after exiting the Collectible prompt they cannot be viewed again.
Why did the Trophy/ Achievement “Mercy” not unlock after killing 5 enemies in Fire Sale? This Trophy/Achievement pertains to the enemies in the parking lot while on the rooftop in Fire Sale.
Can I zoom in multiple times with the sniper rifles? Only the M200 Sniper Rifle has an additional zoom mode.
My ally teammates will not open the door? Move back a few steps. Allies will not be able to open a door if you are blocking it. Also note that your allies may not open certain doors until you have completed the current objective.