Here is the full list of all 36 ValeGuard achievements.
A troop unit reaches max level
Acquire a Harvest Guardian
Unlock the Summoner Class
Defend a town without building a tower
Fight off a bandit attack
Suffer defeat
A hero dies in combat
Complete the ValeGuard Tutorial
Open the Help Menu
Give troops a mount
Give a hero a mount
Repel an undead attack from the graveyard
Build 10 Frost Towers
Complete a campaign without losing any heroes
Complete a campaign on ValeGuard difficulty
Construct a trebuchet
Defend a town without making troops
Train a Templar unit
Acquire 5 enchanted wells
Acquire the Golden Lute
Become the Skeleton King
A hero reaches max level
Destroy a Goblin War Rig
Train a Longbow Unit
Train a Monk unit
Train a Berserker unit
Get the firework effect from a mystery potion
Gain a level from 'Training in a Bottle' potion
Fight off a mushroom invasion
Unlock the Druid Class
Unlock the Barbarian Class
Unlock the Engineer Class
Unlock the Hexblade Class
Unlock the Wizard Class
Unlock the Alchemist Class
Unlock the Rogue Class