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