Final Fantasy XIV’s crossover events with other games give players a chance to obtain mounts, minions, and other rewards. In the case of the Monster Hunter World collaboration event from 2018, Square Enix added an entire Monster Hunter-style fight, with the Poogie minion and the incredible Rathalos Mount offered as rewards.
Unlike some crossovers, The Final Fantasy XIV and Monster Hunter World crossover event is in the game forever. But, you’ll need to have completed the Stormblood expansion and the final quest of the expansion’s Main Story Quest, “Stormblood.”
Once you’ve done this, head to Hearty Hunter in Kugane (X: 9.7 Y: 8.9). Accept the quest “The New King on the Block.” This will allow you to complete the regular Great Hunt Trial. Once you’ve completed it, “The Newer King on the Block” quest will be unlocked. This gives you the The Great Hunt (Extreme) Trial.
Unlocking the Rathalos Mount
The Rathalos Mount comes from the Rathalos Whistle, which is unlocked in two ways. The first is a rare drop from completing The Great Hunt Extreme. The second way is to exchange 50 Rathalos Scale+ with the Smithy NPC in Kugane (X: 9.7 Y: 8.9). You’ll receive one Rathalos Scale+ from each clear of The Great Hunt (Extreme).
Clearing The Great Hunt (Extreme)
The easiest way to clear The Great Hunt (Extreme) is to go in unsynced with a party of level 90. Focus down and kill the Garula add as soon as it appears or complete the mounting Active Time maneuver. With level 90’s, this shouldn’t be too difficult at all. Like Monster Hunter, dying won’t instantly be a game over. Instead, you’ll get three KO’s. Once all three are used, then it’s game over. Also, regular healing spells doesn't work, so you'll have to rely on the potions supplied.
It is possible to solo this fight with a level 90, but the DPS check is very intense. Make sure you kill the Rathalos before its enrage, King of the Skies, or it will instantly kill you. It is recommended that you complete this in the Party Finder unsynced, as it should be a quick grind for a Light Party.