Chosen Assassin | Enemies XCOM 2: War of the Chosen Game Guide

The Assassin is the first Chosen encountered in the game. She's particularly dangerous on short distance, and in this respect, she's similar to the Hunter class - she also uses a sword and shotgun combination. She's also moving a lot, which allows her to cover huge portions of the map within a single turn. Here the similarities end, and the differences begin.

The Chosen Assassin.

The Assassin's camouflage is active during movement - until she disengages it, the player is unable to know where she is (unless you manage to track her; bear with us). She also has the Shadowstep Ability by default, which renders the Vigilance Ability useless. Then, when she approaches a player's soldier, she'll attack with the sword, often stun the soldier, and retreat. This stun is meant to prepare the soldier to be abducted - she can appear next to him, abduct the poor soul and exit the battlefield.

You should keep the following rules in mind when facing the Assassin:

1. Don't ever use the Vigilance ability - she doesn't activate these attacks, so you'll just lose points.
2. She's always in camouflage, but you are able to track her down by placing any unit nearby (just as in the case of aliens revealing your units during the concealment), or by using the scanner. Remember, however, that she won't get revealed until the soldier moves - even if the soldier is two tiles away.
3. She has two ways of stunning your soldiers. Either by using the sword, or grenades. She uses the latter for clusters of enemies. She can then abduct the stunned soldier and flee the battlefield. You should consider using the Specialist's abilities to bring the stunned ally round.  
4. The best strategy is to place the whole team out in the open and waiting out a few turns until the enemy appears there. In the meantime, you can use abilities/items for scanning, or move the soldiers 1 tile in order to increase the chances of revealing her. Once she's compromised, you need only a couple attacks to get rid of her.
5. Don't never ever fight the Assassin in the vicinity of groups of enemies. Try to eliminate regular enemies before facing her.
6. If you own the Alien Hunters expansion, you can use the Frost Grenade/Frost Bomb) - it freezes the enemy for two turns, which lets you get rid of her easily.