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