Board Thread:Questions and Answers/@comment-1807002-20160327050637/@comment-5394165-20160329214820

http://mysingingmonsters.wikia.com/wiki/Breeding_Structure#General_Breeding_Rules

I think this might answer the "what happens if an element is repeated" question.

and my way of looking at it (double of of an element cancels it out) doesn't hold true after thinking on it after sleep. If rares can be produced by doubling up, then they don't exactly "cancel out" each other.