What are some strategies for effectively utilizing MTG face-down cards in gameplay?

One strategy for effectively using face-down cards in Magic: The Gathering is to bluff your opponent by making them think the card is something powerful when it may not be. Another strategy is to use face-down cards as a surprise tactic, revealing them at a strategic moment to catch your opponent off guard. Additionally, you can use face-down cards to protect your more valuable cards or to set up combos for future turns.