At the end of The Dying Lands in Horizon Forbidden West, when you’ve found a way up and reached the Repair Bay Core of Repair Bay: Tau, you’ll find that the Repair Core is guarded by a formidable Grimhorn, and you have no choice but to kill it. It’s not easy, especially if you’ve rushed ahead with the main quests without levelling up as much as you should have (like we did). But even at a lower level, it’s possible to kill a Grimhorn, and here’s how.
A Grimhorn’s biggest weakness is acid, and there are chests around the Core that contain Acid Traps so, before you even activate that node, get those traps and plant them around the room. We also hope you have plenty of Metalbite with you, because acid arrows are going to come in very useful. Acid will corrode the Grimhorn’s armor plating, of which it has a lot, making it easier to target specific components and weak spots.
Purgewater is also effective against a Grimhorn, and will render the machine temporarily unable to use its fire attacks, which will give you a window of opportunity to plant more traps and attack the Grimhorn directly.
Perhaps the most effective strategy against a Grimhorn is to remove its cluster launcher weapons and use them against it. However, those things are well protected by armor, and pretty tough in their own right. We tried to knock them off, but the Grimhorn eventually died from acid damage before we could.
In general, try to keep your distance from a Grimhorn, as this will make dodging its attacks much easier. It’s a big target, so you should be able to hit it from long range, even with a Hunter Bow. If you’re fighting the Grimhorn at the end of The Dying Lands, focus all your attention on it. Varl and Zo should keep the other machines away from you.