Why does the Hog Rider have a green ribbon with only 6 Dark elixer?

For some reason in my troop training, the Hog Rider has a green ribbon across the bottom and is only 6 dark elixir. Why is this? Did I accidentally boost the barracks? It doesn't look like it. Is there a sale going on?

It is part of the Events part of the game .

Clash Of Clans Hog Rider Event

Did someone say Hog Rider?

http://www.itechpost.com/articles/67086/20161220/clash-of-clans-winter-update-hog-rider-event-is-live-christmas-gifts-leaked.htm

The Clash of Clans Hog Rider event offers a very large discount to train Hog Riders. The rewards after completing the challenge are gems and experience. All you need to do is win a number of multiplayer battles.

During these battles, there is a specified number of Hog Riders to be used. The entire Hog Rider event only lasts two days or 48 hours. You could find the details in the Events tab.

Happy Clashing!

There is a new "Events" tab that was added in the new update. As part of this update, the first event they are doing centers around the hog riders. It significantly reduces the training costs for them because the event requires you to use a certain amount in 3 multiplayer battles. If you do, you are rewarded 300xp and 30 gems (which is great because the next event coming up is a 1 gem collector boost :D).