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 6 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.