If there's one thing that collectors like to show off in Final Fantasy XIV, it's their mount collections. Mounts alone can showcase what a particular player is capable of and the Duties they've triumphed, and one that showcases those achievements well is the Deinonychus.
Rather than requiring a currency or completion of an achievement to obtain, the Deinonychus serves as a possible reward from the finale of the Save The Queen adventuring foray, Zadnor. There's no guarantee you'll receive the Deinonychus, meaning you may have to make several attempts to see the rare mount as a possible loot drop.
How to unlock the Deinonychus mount in FFXIV
The journey to obtaining the Deinonychus mount begins with the Shadowbringers "Save the Queen" questline, taking the Warrior of Light through the Bozjan Southern Front and the barren land of Zadnor. By participating in the areas' Skirmishes, Critical Engagements, and completion of available quests, you'll earn Mettle that acts as "experience" toward your Resistance Rank. The higher your Resistance Rank, the more content inside of these adventuring forays becomes accessible.

Once you've progressed deep into the third zone of Zadnor and achieved Resistance Rank 25, progressing through quests will eventually lead you to the quest "March of the Bloody Queen" the "finale" for Zadnor's quests. Here, you'll head into an instanced area known as The Dalriada, similar to the Bozjan Southern Front's Castrum Lacus Litore.
The Dalriada is designed for up to 48 players, though those participating will receive an Echo if the group is significantly undersized. There are four bosses, along with a miniboss gauntlet, depending on the paths taken, meaning you'll need a competent party to make it to the grand finale. When aiming for the Deinonychus mount, your prize potentially awaits after defeating the final boss. While you may feel that your hard work should be rewarded with the Deinonychus Horn, it isn't guaranteed to appear with each completion, leaving you with more Dalriada in your future.

Because the Bozjan Southern Front and Zadnor are longer current content, the number of players participating may leave much to be desired depending on the time. While there's always some activity within the Save the Queen areas, only some are interested in the engagement and may be there for other goals. The best time to attempt is during your server's peak hours, making it more likely to have many players willing to participate. Keeping an eye on shout chat within the zone is one way of tracking when the instances last appeared.