Shadowverse

It’s already the second or third time a dragon has been completely defeated by me. And this time, I was struggling, barely managing, and then suddenly, even for me, the enemy had only 12 health left. I played two cards and placed three cockroaches, dealing exactly 12 damage.
The worst thing is the Wards; I lost because of them against the Sigil Rune. I have a couple of counters for them, but they only work sometimes. Tentacles with Enhance are too expensive, and Pixie Mischief is too unpredictable.