Here is the full list of all 29 Mighty Party achievements.
Sacrifice units 100 times
Achieve 200 rank
Open 5000 chests
Open 2500 chests
Win 500 battles in PvP with Trixy
Achieve 100 rank
Win 500 battles in PvP with Son of Woods
Achieve 1 league
Reborn units 20 times
Achieve 5 league
Win 500 battles in PvP with All-Father
Open legendary chest
Achieve 50 rank
Reborn units 1 time
Open 500 chests
Achieve 10 league
Sacrifice units 1 time
Win 1 battle in Divine Arena
Win 1 battle in Survival
Achieve 20 league
Invite 10 friends
Open 50 chests
Complete Chapter 3 in Journey
Achieve 10 rank
Open epic chest
Invite 1 friend
Defeat first boss in Journey
Complete the tutorial
Win 1 battle in PvP