To increase Kratos’ fighting power and most of all unlock new skills for his terrible battle axe, you’ll need to find several Frozen Flames during the adventure. These legendary resources contain the rage of fire and the temper of ice. They appear after mighty battles and help to upgrade the Leviathan axe.
When you get an Frozen Flame, you just have to go visit Brok or Sindri, the two dwarf brothers who appear at the 4 corners of the realms of God of War. Through their workshop, you can increase your power axe and unlock many battle skills for Kratos. Know that there are 5 levels of enhancement for the Leviathan axe which means you will need to find 5 Frozen Flames to maximize the power of the Kratos axe.
Note that the first 4 are very easy to get, you just have to advance in the main quest of the game to get them. You will win them after a fight on a boss simply and will have to pick them up on the ground. Note that if you accidently forget one, you just have to go to one of Brok or Sindri’s workshops to retrieve the items forgotten in the « lost items » tab.
How to get an Chilling Mist of Niflheim in God of War :
The last Frozen Flame will be harder to get, you will need to have learned the Niflheim language through 4 cipher language codes to open the realm of Niflheim. Then you will have to go in search of an Chilling Mist in this kingdom that you can obtain in the treasure room of Niflheim’s workshop. But for that, you’ll need to get 5,000 mist echoes through the maze of this realm.
Once you have acquired 1 Chilling Mist, you just have to go back to the dwarf brothers to make the exchange of the object with the last Frozen Flames which will allow you to obtain the ultimate version of the Leviathan axe.