Here is the full list of all 20 Hero-U: Rogue to Redemption achievements.
Became a student at Hero-U
Won Rogue of the Year
Explored all of the Castle's common areas
Explored all the Hidden areas in the Castle
Explored the Dungeon and Catacombs
Explored the Sea Caves and found its treasure
Best Friends with Professor Gerhard
Best Friends with five or more people
Played like a Paladin by helping everyone with their personal quests, achieving Mr. Popularity, and achieving Teacher's Pet
Found True Love and gave a One and Only Ring to your lover
Killed one of every monster type
Defeated every boss in combat
Completed the game without killing anything
Made at least two enemies and joined the Thieves’ Guild
Helped all of the ghosts: Burgundy, Chianti, Patrick, Emily, Jamus, Hans, Leo, Alex, and Issac
Raised at least five stats to 100
Raised at least five skills to 100
Completed an advanced elective course and passed the final exam
Beat Sosi at Billiards, Katie at Darts, Esme at Cards, won at least one game of Poobah, and reached at least 50 Luck and 75 Gaming
Befriend the Kwirk