After decorating this location, Mr. McScroogle (equal level) will spawn and attack you; kill him. (If a Dread Guard happens to wander by and kills McScroogle before you do, don't panic; just wait a few minutes, the green shiny will reappear, and you can gather it when the guard isn't nearby and McScroogle will respawn.)
Return to Gevil, the Gigglegibber tree merchant in Neriak, to claim your reward.
This article refers to events, personae and activities only present in-game during the annual Frostfell celebration. Frostfell comes to Norrath each year from (roughly) the second week of December to the first week of January.