Board Thread:DC Wiki Discussion/@comment-1738746-20150620094347/@comment-1738746-20150624145819

They weren't initially created with the idea of a Holiday dragon in mind- when first created, they were available all year round. At some point, they only became available on Halloween (this date I don't know, all I know is that the change was never officially announced). Holly Dragons were the first intentional Holiday dragons. Either way, I realised that we don't get much traffic on these forums so I took it up on the DC forums and got a reply from TJ09- he doesn't seem to consider the Undead belonging to either category, so I think "Rare" is a general enough term to suffice the wiki's need to fill in a Rarity status for each dragon.