Here is the full list of all 27 Great Hero's Beard achievements.
Max out all princesses
Defeat the Chubby Tubby Warlord
200 ATK SPD
10th Retirement
Defeat the Sea King Neposeitune
Defeat the Avalanche
Defeat Skelethrone King Slayer
Defeat Demon Lord Baal
100'000 HP
5th Retirement
Defeat the Guardian Azriel
First Retirement
Rescue Fifth Princess
Reach Level 100
100 ATK SPD
Rescue 4th Princess
Reach Level 80
100'000 Damage
Deal 1M Damage
Rescue Third Princess
Reach Level 60
Rescue Second Princess
Deal 1'000 Damage
Reach Level 40
Reach Level 20
Rescue First Princess
First Fusion