During the Advent Calendar, a player will receive the Stone Pack upon successfully completing the level.
A few hours after The Elf Mine was added to the Advent Calendar, a small part of the level near the beginning was altered to make it easier for beginning players to understand how to get a Blue Coin.
The level contains 21 gold coins and 6 blue coins scattered throughout the level. Some of them require jumping into the teleporter, which will teleport you to a random area on the map. In order to access the teleporter, you must first gather all 6 initial blue coins.
This world has since been incorporated into another world made by Minimania, which can be found here.
You can play The Elf Mine here: