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