At level 30 or above, speak with the Wandering Minstrel in Eastern La Noscea (1.0)
Use the odd-shaped horn gifted to you by the wandering minstrel to call a massive goobbue to your side.
Traded for a song by the High Satrap of a distant land, the secret to taming these creatures once thought to be unbreakable was introduced to Eorzea by a mysterious wandering minstrel who journeyed through the realm in the final days before the Calamity.
Would that I had the girth of a goobbue! - Nanamo Ul Namo