The Z-Rex is an extremely fast and agile boss while having small weak points that you must hit to deal maximum damage. Keeping your distance and avoiding running in a straight line, continuously breaking line of sight with the boss, is the best way to avoid it catching up to you and inflicting damage. You should only turn around and do damage when you are on the other side of the arena from the boss, it is opening its mouth to vomit out Toxic Zombies, or it currently has some Toxic Zombies attached to its side that, when shot, will deal 24,000 damage to the boss instantly.

For weapons, the Ray Gun MKII-Wraith Fire is by far the best variant for this boss fight due to its fire rate, damage output, and range. Paired with the Wunderwaffe DG-2 for clearing out the zombies spawned in the boss fight, it can make your time much easier.

For more information on how to complete the main quest, prepare for this boss fight, and defeat the final boss, you can read our detailed main quest guide for Shattered Veil.