Available in store during Halloween Week. Its quite cheap, and you can get an random Halloween item.
▶Available in Store
Gift of Growganoth ( 200/500 )
"Available only during Halloween! Would you like to donate to the cause? Give Growganoth a few gems, and it will reward you with vast power beyond imagining! Or, perhaps, a random Halloween item. Buying this is equivalent to feeding an item of rarity 75 into the Maw of Growganoth. What you will get is random, so don't buy unless you're ready to be surprised!"
As of 2014, this shop item costs 500 gems rather than 200.