Are there any good counters for a minion spamming Abyssian deck against Abyssians with shadow creep?
In general Cassyva counters Lilith, so there's not much you can do about that.
However, there are some ways to increase your chances.
Lightbender is a good counter to Cassyva in general. He is a 3/3 that dispels all the spaces around himself. Use him to neutralize entire shadow creep swamps.
Secondly, try never to give Cassyva 1 hp minions to use her Bloodborn spell on. I know it's tough with Lilith because you're always summoning those little imps, but if you can, pay attention to when her BB spell is about to be up, and if necessary suicide them onto her or something else so that she can't cast it. The less shadow creep you give her, the weaker her late game will be.
Finally, always pay attention to when she is about to have 7 mana. When she hits 7 mana, you know she will be able to cast her ultimate spell, shadow nova. Shadow Nova fills 4 spaces with creep. This means that it does 4 damage at minimum to four tiles, but probably even more if she has more shadow creep.
You need to place yourself and your minions in such a way that she can't hit all of you. Make sure you don't have any minions (or yourself) within 4 square tiles of each other. Doing this will force her to pick a single target, which will often prevent her from casting Shadow Nova at all, potentially winning you the game.
One of the best counters to Cassvya is just to kill her quickly. The longer the game goes, and the more shadow creep that hits the board, the stronger she gets. Use your Lightbenders to clear the board as much as you can and finish her quickly.
Also, if you have any copies of him,
Archon Spellbinder is a good counter to her as well, because she's typically a very spell-oriented character.
Also, I think you had asked me about my thoughts on the new cards, how to play them, how they would affect the game and all that. I'm not experienced enough with the game to give a satisfactory answer, but
here's an article on it.