A code has been revealed by Japanese show Pokémon Get☆TV that allows players to unlock Contrary Serperior in Pokémon Omega Ruby & Alpha Sapphire.
This isn't a one-time deal, either -- the code can be used by multiple users while it remains active.
The code is POKEMON497, but don't go rushing for your 3DS console just yet, as it's not active until January 9th, 2015. However, once it goes live, you'll have until November 30th 2015 to input it -- which should give you plenty of time.
UPDATE: We've had plenty of people asking if this code will be region-locked -- seeing as there's never been a code like this before (previous region-specific codes have been single-use) it looks like we'll have to wait until the 9th to see if this is a worldwide deal.