Ice axe

 was introduced in Game of Crone DLC. It is rewarded upon completing the revolution quest line with Donkey.

The equips to the  slot and is used when mining.

Efficiency represents how much progress toward an operation each swing of the axe provides. A 100% efficiency would cause something to progress at the normal rate while 200% would mean it progressed at twice that rate. The has an efficiency of 200%.

Energy usage represents how much energy each operation consumes. The requires only  per swing.