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