Define "set in motion."

The phrase "set in motion" specifically refers to moving a scheme card off the top of your scheme deck and turning it face up. This action initiates the effects associated with that scheme card, allowing players to benefit from the game-altering effects provided by the scheme.

In a game of Magic: The Gathering, scheme cards are part of the "Archenemy" format, where these cards represent powerful schemes that a player can employ against their opponents. To "set in motion" is a crucial step in activating the card’s effects, making this action necessary for gameplay within that context.

Other options do not align with the definition of "set in motion." Discarding a card from your hand, putting a scheme card into your graveyard, or taking a card from your graveyard and returning it to the deck involve different game mechanics that do not pertain to activating a scheme’s effect. Therefore, the action most closely associated with "set in motion" is indeed moving the scheme card from the top of the deck and revealing it.