Board Thread:Questions and Answers/@comment-24577221-20140405151723/@comment-7326455-20140413203135

As I understand it, for the limited-edition monsters that are bred using four-element and three-element parents, then while the limited-edition monster is available, it's possible - with a very small probability - to get the four-element monster as a result of a failed breeding. Never been sure if that's a bug or not, though.

Never seen or heard of it happening otherwise.