Interesting concept. It is basically an expensive dragon with better stats, but the fact you have to "sacrifice" a creature is a good way to balance it. I agree on a cost reduction for the upgraded. 12 seems fine; maybe even 10 for the unupped and 11 for the upped, because a 2-card-combo isn't easy to bring up early. I mean, they are actually dragons with health boost, but still vulnerable to Freeze, AM, RT and BB.
What happens when targetted with Reverse Time?