>.< 10 , 18 , 7 , 3 . 5 cards. Good luck with that.
Fixed.
Also, it's not THAT unfeasible. A rainbow deck designed to tear through the deck for this combo could do it fairly easily. It would just have to be able to stay alive until then.
I agree with Nepycros.
We cannot really evaluate cards based on some highly unlikely optimal result where you get all the cards and quanta you need, while your opponent for some reason does nothing. There are millions ways how that one-shotting you talked about would fail.
We could come up with all kinds of possible scenarios of what might happen, but it is impossible to say how powerful the card really is, without actually testing it. Some cards that sound OP in paper, might not turn out to be not so OP after all, and vice versa.
Card cost and damage can always be tweaked. They only way I see how this idea would totally fail, would be if there was a simple and cheap way to wake these guys up. That would make it beyond repair.