Forza Horizon 4

To unlock this achievement, you must own the Fortune Island DLC, and progress through the Island Conqueror Horizon Life stat. To reach round 10, the final round, you must earn 168 thousand influence from race events around the island. I would guess this would take the average player around 3 to 4 hours of playing time if that.

Once reaching round 10, you will also unlock The Leviathan and The Kraken. These are the equivalents of the events you unlock once reaching round 10 in road, dirt, or cross country racing.