It's like you can't say anything about a deck or card without someone jumping in with the dismissive 'lol, u just bad, l2p' or 'you're playing wrong' as if any card/deck can counter any other card/deck in any situation with ease. I'm not saying anything is OP, I just noted that this specific deck is hard to beat in a lot of situations.
They can stall with Ice Lance from turn one. They can stall with Frostbolt from turn 2 or combo it with Ice Lance from turn 3 for 7 damage. They can stall with Mirror Image from turn 1 or double Mirror Image in later turns; that's four minions you need to attack before being able to attack their hero. From turn 3 they can freeze your entire board with Frost Nova. From turn 3 they can play Ice Barrier which effectively gives them +8 health per barrier to stall. From turn 3 they can also play Ice Block which makes them immune from lethal. From turn 4 they can stall with Cone of Cold and play Fireball to your face if they feel safe. Turn 6 they can stall with Blizzard and kill low-health minions with it. Turn 7 they can clear your board with Flamestrike and at turn 10 the Pyroblast comes out.
If they get good draws, they can stall on every turn and do a lot of damage to you in a short time without you being able to counter.
I was playing miracle Rogue and would have killed him next turn if he had not had a second Ice Block up (already burned through one Ice Block and two Ice Barriers) and Pyroblast in his hand.
EDIT;
Again; not saying anything is OP, it's just hard to counter in a lot of situations. Whether this is because of the specific deck I'm playing is fine to bring up, but no need to go 'You're playing wrong' or 'Should not kill you' to imply that it's all just down to me and my 'poor' playstyle and 'bad' deck without knowing how I played or what deck I played or any further context.