What are you trying to do? Have you drawn every other minion from your deck and completed C'thun?
For Vanndar to work your other minions in the deck need to cost more than him - so they need to cost 5 or more. Your deck has only one minion that costs more and it would probably not be discounted as it would not actually be in the deck.
I guess you might have thought that all other minions must cost less?