The Leviathan Axe was made by the Dwarven brothers Brok and Sindri, specifically forged to fight off the power of Mjolnir after feeling responsible for the destruction caused by Thor.
It was infused with the echoing screams of twenty frost trolls (give or take), and has several runes inscribed on the blade that grants different powers.
Among it's powers, the Axe has ice magic, capable of creating and shooting ice, freeze almost anything, bring ice storms and more related abilities. It is bonded to you and can be called back to your hand via mental command from any distance, even through dimensions and universes.
The Axe is strong enough to fight Mjolnir, being it's equal match in power.