You get this for beating the final boss of the Frost Adventure campaign. Keep advancing the campaign until the peak appears as an objective on your map. You’ll want to be at least level 10 and have lots of healing items, focus herbs and four tents. Having someone with Party Heal and the best pipe is helpful too.
The peak has 3 encounters plus an area to rest as a fourth encounter for a total of four levels up the peak. You fight against the boss on the fifth level by itself. It’s level 10, has 12 physical and magic armor, and around 600 hp. It’s immune to freeze, stun and shock. Bleed and ignite work though. Remember that you can use most items during each party member’s turn plus do an action so ahead of the battle, spread out your buff herbs and items - the campaign ends after this so don’t hold back.
The boss casts entangle and freeze on your party, and it’s attacks frequently do splash damage against you. If you have the ability to increase group armor, resist or evade then do that to help. You can also do Reset and Slow against it, and increase your speed and Rush so you can get more turns in.