The Sticky Stealer is a dragon species mentioned once, in The Incomplete Book of Dragons.
Only the egg of the Sticky Stealer is shown in the Incomplete Book of Dragons. No description is given. However, based off the picture of their egg and the 'sticky' in their name, these dragons may be gooey in some way.
Nothing is written about the Sticky Stealer's abilities. It might be inferred however, that this dragon is a very good thief, based on the 'stealer' portion of its name.
A Sticky Stealer egg appears in the "Dragon Eggs" section of this How to Train Your Dragon Book series Reference book.