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