For those who are wondering what wraiths are, they are aliens which have the ability to go invisible. When they turn invisible, they term them as “re-sheath”, meaning that they 95% of the time will appear right in front of you and start charging their attack. If you start shooting them they will stop and disappear because they are very careful and they have relatively more health than other enemies in the same class.
Now the goal in this mission is to kill a wraith before it re-sheaths.

Step by Step

Below are some tips you should better read before starting this mission:

1. I suggest using Impact. This is most probably the best way is to blast them away as soon as they appear, this way there will be a few seconds available to you to run towards them and blast away with your shotgun before they get up and disappear again.

2. On the other hand, there are a few other weapons that work well if the shotgun isn’t available such as the magnet gun but I highly recommend you to use it for it is very good at dispatching enemies of that class/size, especially with the weapon upgrades that affected it like Stopping Power.

Supplementary Video: