Here is the full list of all 22 Flynn: Son of Crimson achievements.
Completed all levels, acquired every relic and learned every skill.
Defeat Zealock
Complete the 6 challenge stages.
Acquire every skill from Loretta.
Defeat Imbra the Shadow Sorceress.
Find, collect and sell all 20 relics to Yombal.
Find Bax in 4 separate locations.
Defeat a training dummy in Sanctia.
Defeat Xellios the Toxic Marksman.
Have an enemy frozen, burned and zapped simultaneously.
Defeat Rozia for the final time in the Desolate Woods.
Perform a full plummet combo with any Crimson weapon.
Have a throwable rock bounce on an enemy 5 consecutive times without touching the ground.
Starting with an uppercut, perform a full aerial combo with any Crimson weapon.
Chain zap 7 enemies with lightning magic.
Using the sword, pogo-bounce on 4 separate enemies without touching the ground.
Defeat Kravios the Aquatic Voltknight.
Defeat Bora the Whirlwind Assassin.
Acquired your first skill.
Find and collect a golden relic.
Quickly skip Bohrin's dialogue.
Set out on an adventure with your beloved friend, Dex.