There is no guide for this game yet. But apparently it is EASY POINTS!  

The Easy Way - 100 points
Complete game in easy difficulty
   
The Normal Way - 150 points
Complete game in medium difficulty

The Infernal Way - 200 points
Complete game in hard difficulty
   
Infernal Power - 10 points
Obtain Infernal power
   
Teleportation - 10 points
Obtain Teleportation power
   
Multiple Teleportation - 10 points
Obtain multiple Teleportation power
   
Mana Booster - 30 points
Find 3 mana boosters to increase your mana
   
Health Booster - 30 points
Find 3 health boosters to increase your health
   
Betrayal - 20 points
Complete Prologue
   
The Dark Angel - 20 points
Join the Abyss
   
The Cloister - 20 points
Get inside the cloister
   
Cable Ride - 20 points
Get to the upper cloister
   
The Acolytes - 20 points
Survive the upper cloister
   
Walls of Pain - 20 points
Complete mission 1
   
The Chase - 20 points
Find Elena
   
Duel - 20 points
Defeat Elena
   
Going Down - 20 points
Find Wolf's lab
   
Heaven's Triumph - 20 points
Complete mission 2

Steelworks - 20 points
Enter the Steelworks

Running Man - 20 points
Complete mission 3
   
Wings of Steel - 20 points
Find the plane

Reflection - 20 points
Find the device in the plane
   
The Resurrection - 20 points
Find Barbara
   
Airstrike - 20 points
Complete mission 4
   
The Island - 20 points
Find the Observatory
   
The Saint - 20 points
Complete Mission 5
   
The Cowboy Way - 20 points
Find Dual Pistol
   
Fire Away - 20 points
Fire rocket launcher 20 times
   
The Dark Force - 20 points
Use infernal powers 100 times
   
Precision - 20 points
Don't activate the gas traps in the plane
   
The Collector - 20 points
Retrieve energy from 100 enemies