FFXI wiki icon Ambush is a Thief merit trait in Final Fantasy XI. It is a group 2 merit, meaning it will initially cost 3 merit points, then 4 for the second rank, and 5 for the last. Each rank boosts melee and ranged accuracy by 3 when attacking from behind. This trait is active so long as the thief remains level 75 and not participating in a level-capped event.