Awesome idea, I like it. It's great to have extra challenges, please give us more in the future.

Some improvement suggestions for the next challenges:

Button to start
Simply offer a button in the game which starts this special challenge mode and makes sure that all rules are kept.

Meltdown
Also offer a special meltdown challenge. Meltdown is such a great format, I love it. But - honestly - it is a bit frustrating to play because you have to wait so long till an opponent joins meltdown. I'm sure that this will push the format with much more players to play the meltdown format.

In-Game announcement
New challenges should be announced not just at social media and forum, it should also be announced at the in-game "News and Announcements" when you start the Shadow Era App or game client.