Here is the full list of all 27 Little Adventures achievements.
Get the Guard
Get the Princess
Get the TNT Upgrade
Get the Tank Upgrade
Get the Crit Strike Upgrade
Get The Packed Upgrade
Get the Cold Spell Upgrade
Get the Cold Kill Upgrade
Get the Poison Upgrade
Get the Freeze Upgrade
Get the Stun Upgrade
Get the Lifesteel Upgrade
Get the Thorns Upgrade
Get the Golden Cape Upgrade
Get the Explode Upgrade
Get the Blood Explosion Upgrade
Get the Ekstra Health Upgrade
Defeat the Last boss on difficulty 5
Defeat the Last boss on difficulty 10
Defeat the Last boss on difficulty 15
Defeat the Last boss on difficulty 20
Defeat the Last boss on difficulty 25
Defeat the Last boss on difficulty 30
Defeat the Last boss on difficulty 35
Defeat the Last boss on difficulty 50
Defeat the Last boss on difficulty 75
Defeat the Last boss on difficulty 100