From Webkinz Insider Wiki
Boiled Wyvernacle is an unsolved stove secret recipe.
The four other recipes in this batch have been confirmed as stove recipes.
Boiled Wyvernacle holds the record for the secret recipe that has been unsolved the longest. It surpassed the previous record holder, Yummytummy Tumbler, on June 18, 2012. It is also one of only two secret recipes that have been unsolved for over two years. The other recipe to reach that milestone is the aforementioned Yummytummy Tumbler. Webkinz Newz gave three hints for this stove recipes. The first clue was "You get this ingredient once a year" the second clue was "Something on a stick". The third clue is unknown at the moment.
The Webkinz Newz has this to say about the recipe: "This is one sweet stew! It might look a little curious, but it tastes just lovely!"