The enemy with the strongest melee attack in XCOM 2 is undoubtedly the Berserker.
This female monstrosity, which also appeared in XCOM: Enemy Unknown but has been greatly enhanced in XCOM 2, is merciless and has the potential to become enraged, increasing her attack range and damage output. If any unit – whether they be ADVENT or XCOM – gets too close to an enraged Berserker in XCOM 2, she will lash out with her powerful melee attack.
Keep this in mind, Commander, as it may prove vital when plotting your higher-level tactics in XCOM 2.
Previous reports on enemies: