Here is the full list of all 29 Mighty Party achievements.
Open 50 chests
Achieve 10 rank
Complete Chapter 3 in Journey
Open epic chest
Invite 1 friend
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 500 chests
Open 2500 chests
Open 5000 chests
Win 1 battle in Divine Arena
Win 1 battle in Survival
Achieve 20 league
Achieve 10 league
Achieve 5 league
Achieve 1 league
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 10 friends