How about this:
My group couldn't get enough players to start a normal campaign, so we used a couple of Pre-genned level 20s and fought the Gargantuan Dragons.
It started out smoothly enough for me, the DM. Then they started crittig every round and not once, but twice drew into a dex damage card. So then we had this gargantuan CR 25 Blue go down in round 2 after suffering 10 dex damage.
Aggravated, I was like "okay, the colossal red one swoops out of sky. Roll initiative." During round 2, they dazed it. Next round, they stunned it. Third round, they killed it. That's right, they killed a CR 28 Dragon in 3 ROUNDS using the deck.