It would certainly change a lot, which is what testing is for. A card to balance the change should also be considered. Or many nerfs can be made, such as two shields with 75% proc efficiency and 50% defense status (rounded up). So a spine tharapace and a permafrost would give 2 defense and 75%^2 poison proc and 75%*30% freeze proc. I still dubscribe to a fire card granting a second weapon slot, and have it get momentum. Oh, see? momentum passes both shield, and is common enough as is. Bam, balanced.
Tell me about the quanta it consumes to cast dual buckler with 2 powerful shields. In the best case, 3-4 SN. Therefore, 3-4 turns at least just dedicated to play shields. You would need a very good draw to do it in any deck and you risk of being PC'd and all your shield-based strategy is screwed.
It's a powerful card with high risks, very balanced and brings lots of new strategies.
That said, about getting 2 shields with the same effect, like fog and dusk, a little "Shields with same effect abilities are reduced" text wouldn't come bad.
Mhhh... maybe you're right about reducing same shields effect. A dual Hope would grow too fast: 3 photons and you could block 6 damage!
5 photons and you block a dragon!
This would generate a new rol/hope deck that could work without Fractal.
Even simple vanilla creatures with Luciferin could block almost anything.
Try to think to a
deck with frogs, cockatrice, hopes and luciferin and dual buckler. Rushing with high defense, invulnerable to PC!
But very vulnerable to CC, so maybe it's not OP anyway.
I like this card anyway!