https://www.gamespot.com/articles/monster-hunter-worlds-rathalos-appearance-in-final/1100-6460438/

Monster Hunter: World is crossing over into the realm of Final Fantasy XIV, and vice-versa, with two big iconic monster fights. Final Fantasy players can take on a Rathalos and earn themselves armor and a mount, while Monster Hunter players can take on the Behemoth.

A new trailer showcases the Rathalos fight against four players. Beating the Rathalos appears to grant you some Rathalos armor, distinct from the Monster Hunter armor set, as well as a Rathalos mount. You can start taking on the encounter at the Azim Steppe on August 7.