Morceau de charbon

While doing Instant Adventure in the zone, you'll sometimes get sent on a Fae Yule themed adventure arc. The quests will all be centered around the Yule Village and completing the quests builds up the Village. At the conclusion, all the vendors will be there, including the unique Dimensions vendor. Once built up, the Village remains for an hour or until a new group starts a Yule themed quest arc (whichever happens first). If it helps, you can look on your map of Freemarch - if the Village is currently active, it will show a unique Yule icon on the map at the site of the Village. As an aside, the chance to start the Fae Yule IA arc is random, but in my experience it usually pops up every 3 or so quest arcs in FM and SW. The zones that include FY villages are: Freemarch, Silverwood, Scarwood Reach, Pelladane, Cape Jule, and Ashora.

Locate the Fae trees with presents around the base of the tree and Fae marching around the trees. Get in close to the trunk of the tree so you can click package stacks without having to move. Click the stacks of packages (not the single packages) to get the snowflakes, with the rare chance of getting this lump of coal. Take the coal to Greatfather Frost's fireplace by clicking the brazier in his hut near Sanctum or Meridian or possibly in the instant Adventure Father Frost hut. Naughty, Definitely Naughty is the achievement for burning 10 lumps in this manner.