For a limited time, you can unlock a special Horizon: Zero Dawn costume for your Palico. It turns them into a Watcher robot from Horizon: Zero Dawn, including the Watcher grinder melee weapon. To get it, progress through the game until you reach HR six or higher, and select the "Lessons Of The Wild" special event. This arena fight requires you to fight eight flying Barons, which is not too hard. You will be rewarded with a watcher lense. To get the full Watcher body armor and Watcher grinder, you need to complete the event three times to get three watcher lenses.