Here is the full list of all 15 Feral Flowers achievements.
Beat Big Boi
Beat Scourge
Beat Big Boi II
Beat Mother Flower and clear the game
Clear a warpless run
Collect 10 rare quince in a single run
Clear a 100% run
Find the Rake of Justice
Find a red quince
Perfectly time a boost off an enemy
Scale the 3-6 question mark
Backtrack to the 1-1 red quince
Activate and collect the 9-1 red quince
Clear the game with all red quince (and that's about it)
Complete a 105% run