Here is the full list of all 25 Knight vs Giant: The Broken Excalibur achievements.
Complete the tutorial
Equip an active blessing
Use a teleport
Defeat 10 Rocklings
Defeat 3 Wilkin Savages
Defeat the Wilkin Champion
Defeat the Rockflesh Treant
Defeat the Forest Giant
Equip a gem
Increase Arthur's abilities in the skill tree
Defeat the Arcane Monolith
Defeat the Desert Giant
Receive a flower blessing
Upgrade a weapon
Defeat the Lava Giant
Defeat the Void Giant
Defeat The Architect
Reach kingdom level 2
Reach kingdom level 3
Reach kingdom level 4
Unlock Bedivere's statue
Unlock Tristan's statue
Unlock Gawain's statue
Unlock Percival's statue
Recruit the blacksmith