The new card called Goblin Cage can be won in the "New Card! Goblin Cage!" challenge. You can get it when you reach 10 wins in the challenge. The whole challenge ends at 15 wins with nice emote to get.
About Goblin Cage - It is a building that costs 4 elixir. It is a rare card. The building itself does nothing, but when it's destroyed a "Goblin Brawler" spawns and attacks the enemies. He can attack ground troops, not air. The Brawler level is the same as the Cage's level. If you didn't win the challenge the card will be unlockable from Arena 12 (Spooky Town) from 3rd June.
Cage hitpoints: 800
Lifetime: 15 sec
Brawler hitpoints: 853
Brawler damage: 211
Hit speed: 1.1 sec
Speed: Very fast
Note that the stats are at tournament cap (level 9).
Animation video about the new card from the official CR YouTube channel: https://www.youtube.com/watch?v=V0aiyH0uf8I
I personally think that the card is useless, but we'll see how it's gonna develop.
Here's a video from Orange Juice about using and countering the card: https://www.youtube.com/watch?v=eNodzo5Pfok&t=122s