Here is the full list of all 8 Flight of the Paladin achievements.
Hear all music in Survival Mode
Complete the Campaign Stage "The Hollow Road"
Obtain a score of 10,000 Points in Survival Mode
Complete the Campaign Stage "The Woods"
Defeat 100 Monsters in Campaign Mode.
Survive 60 seconds in Survival Mode
Complete the Campaign Stage "Ruins of the Count"
Defeat all three bosses in Survival Mode in one playthrough