Mission/Secondary Objectives

Secondary Objectives are random events that force the player(s) to change plans.

Lockdown
Sometimes enemies will activate "lockdown." This closes most doors, and players have to hack a control console to open them back up. However, this does not lock elevators. Depending on the situation, a lockdown can actually be beneficial for the player by locking out additional enemies and locking in of him/herself with a fixed number of enemies in the room, or put the player in serious trouble by the locking in of him/herself with said fixed number of enemies.

Note that enemies have to run to a control console themselves to activate lockdown. Killing them before they reach the console can prevent a lockdown.

Key Search
Sometimes when encountering a locked door, players will have to search for a keypass before they can proceed; the keypass itself takes the form of a datamass and is picked up in much the same way. However, the rifle can still be used freely after acquisition. Once the keypass is obtained, the locked door can be opened and the mission continued.

Timed Extraction
Certain mission types can trigger a timed extraction upon completion. When you reach your goal, a timer will activate. If players do not reach the extraction point before the timer runs out, they will fail the mission. This is most problematic if an additional objective is triggered, especially a rescue mission.

Additional Objective
Sometimes when players complete their primary objective (or even before the primary objective is completed), they will be informed that there is second primary objective. This can be any of the main objectives, even duplicated ones. This objective is usually pre-determined at the start of the mission as you can explore the area of the second primary objective ahead of it being set as the current primary objective.

For instance, the players have destroyed the reactor core, but instead of being given the extraction location, they are given the location of a hostage, and are required to rescue them before they can be extracted. This can coincide with the timed extraction event, making for a hectic run.