Board Thread:Questions and Answers/@comment-24185163-20131118234228/@comment-27634852-20160204001741

You have to get all the one's it lists in the inventory of the hatched Wubbox, usually one of every monster listed in the market, except the ethereal. You can hatch all new monsters - to put into a Wubbox, that's a good option because it would not have used any of your food yet.

The ethereal island Wubbox does need the ethereal monsters, and the monsters available only in ethereal island.

The first Wubbox I got was on ethereal, once your able to get two different ethereals there it becomes easier to populate that island and get shards. The other Wubbox I got when they went on sale. I think it's better to wait until at least level 40 to try and get a Wubbox, except for the ethereal one, I started it around 35.