https://www.gamespot.com/articles/monster-hunter-world-horizon-zero-dawn-armor-how-t/1100-6457070/

After much anticipation since its initial reveal, the quest to unlock Monster Hunter World's Horizon Zero Dawn crossover Aloy gear has finally gone live. The first content drop earlier this month gave us the Palico Watcher armor. However, this last quest finally unlocks Aloy's armor and bow. If you're curious about how the process to unlock them works, we've outlined the timing and quests below to access the extras.

It's important to note that the Aloy armor set and bow is only available from February 28 to March 15, so if you're keen to get them, you'd best nab them as soon as possible. Unlike other armor in the game, you have to wear the entire Aloy set together--you can't just wear the pants or chest alone. And the set will also alter your appearance so that your character looks like Aloy from Horizon, complete with long red hair.