Shadowverse

You can organize a brawl tournament in Heroes of Might and Magic, and this was done even in Heroes V. The drawbacks are that not every week does the brawl feature a mode where cards aren't needed; sometimes you have to assemble a deck. Up until the day the brawl opens, no one knows what mode will be available that week. Plus, not all modes are equally interesting. Right now, for example, the decks consist of completely random cards (this week, we didn't come up with anything new, so once again, here you go). Added 3 minutes later

unlimited storm haven

Amulets that hatch minions *without* Storm, in a *Storm*-deck, is an "excellent" idea. (I'm certainly quite the expert on unlimited, I last played in the previous unlimited grand prix, but something immediately came to mind.)