Here is the full list of all 20 Paladin achievements.
Kill boss at end of level 40
Collect a total of $100,000 cash
Kill all aliens on level 35
Collect a total of $50,000 cash
Kill boss at end of level 30
Score a total of 500,000 points
Kill all aliens on level 25
Kill boss at end of level 20
Kill all aliens on level 15
Score a total of 100,000 points
Kill boss at end of level 10
Collect a total of $5,000 cash
Score a total of 50,000 points
Kill all aliens on level 5
Score a total of 25,000 points
Fill the rage counter to 100%
Collect a total of $1,500 cash
Fill the rage counter to 75%
Fill the rage counter to 50%
Fill the rage counter to 25%