Crazy idea, but how about something like this:
"When this card is discarded from your hand, also discard the bottom card of your deck."
Still denial, but not so amazingly powerful that it shuts down a deck if done early. If anything, it would complicate the end game for the opponent by putting them on the clock (excuse the pun) to win before you can stall them out of cards. Given that we can already interact with the top card of the deck via Reverse Time, Eternity, and Mindgate, it shouldn't be too difficult to code for bottom card interactions either.
This would also go interestingly well with a possible buff to Nightmare I proposed:
"Add 8 copies of target creature to your opponent's hand. If this would cause their hand to be full, add the remaining copies to the top of their deck."