Focus more on sigils that are either very common or very important to a card's function. So for example: Flying, Brittle, Burrower, Guardian, Fledgling, Touch of Death, Worthy Sacrifice, Many Lives, Bi-furcated and Tri-furcated. Sigils relating to Mox and Energy are obviously not a priority as those costs weren't added yet.
Now that I'm making a comment, I have a couple of ideas. I haven't tested the new version yet so I don't know if you've changed it, but there should not be "live overkill". I.e. when you deal more than 5 damage in one turn, the extra damage should not carry on to the next live on that same turn. It's not present in the base game in any of the acts, as it's essentially the same as giving each player 10 health and doesn't prevent OTKs. In terms of coding, it means that the player damage should be calculated after the battle phase ends, not after each individual attack.
Also, will you add actual matchmaking? Or, at least, make rooms that people can join without an IP address? Sorry if it's stupid to ask but I don't know how any of this multiplayer stuff works.