The Senna Forever Add-on for Horizon Chase Turbo has 11 achievements.
Finish all races of Chapter 1: Debut
Finish all races of Chapter 2: Breaking Limits
Finish all races of Chapter 3: Ascension
Finish all races of Chapter 4: Challenges
Finish all races of Chapter 5: Prestige
Win on Portugal of Chapter 2 collecting all coins, using 4 nitros and with a perfect start
In Japan of Chapter 3, win the race collecting all coins, all in the same race.
Accomplish all Senna’s Marks of all races on Career Mode.
Win a championship on Newcomer Category
Win a championship on Challenger Category
Win a championship on Legend Category