Here is the full list of all 15 ReMix:Prologue achievements.
Complete 0 difficulty with any hero
Complete difficulty 1 with any hero
Defeat 100 musical monsters in total
Defeat 500 musical monsters in total
Defeat a total of 1,000 rhythm monsters
Use Yinyin to clear any level of difficulty
Use Hehai to clear any level of difficulty
The team reaches level 5 in a single game
The team reaches level 20 in a single game
The team reaches level 25 in a single game
The team reaches level 30 in a single game
Completed 5 waves of battles in total
Completed 15 waves of battles in total
Completed 30 waves of battles in total
Unlock 1 echo clue