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