Depending on the intended mechanics I like the idea of this card.
Is the damage reduction per attack or per turn based? Is this stacking? Does stacking affect the odds of breakage?
I would assume that the upgraded version would generate an upgraded dragon?
its a shield, so no stacking and the damage reduction is per attack.
yes upped would produce and upped dragon
Diamond shield on itself cost 6 and blocks 3 damage only, and it is upped. So I could imagine unupped version of this cost at least 9 , while the upped one's cost at either 9/10 if it releases upped dragon.
diamond shield also stays until destroyed as opposed to just breaking, so its not the best comparison. in a lot of cases, this card with block a few attacks, and essentially become a dragon you have to wait a turn for. abuseable in some situations yes, but the chance of breaking is not dependent on the attack of the monster, so it should break quickly enough.
now that i think about it, the chance of the dragon "coming out alive" doesnt have to be 100% id prefer to balance it that way than raising the cost.