Legendary

Legendary cards have a gold border and are the hardest to obtain in the game.

They could be obtained at the monthly calendar after logging in a certain number of days. These cards can be upgraded only up to Level 12 and when you get them, they start off as Level 9.

They are mostly found in Legend packs but they are discoverable in most other packs as well. Though it doesen't happen often, there is a small drop rate.