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When you set this scheme in motion, for each opponent, create a 3/3 black Horror creature token that attacks that player each combat if able.
Each Horror token can attack only the player it was created for. It can’t attack a planeswalker that player controls.
If one of these creatures can’t attack its player during a given turn (perhaps because that player has left the game, or because a member of the opposing team has gained control of it), it may attack another player, attack a planeswalker an opponent controls, or not attack at all. If there’s a cost associated with having that creature attack its player, you aren’t forced to pay that cost, so it may attack another player, attack a planeswalker an opponent controls, or not attack at all.
If two or more effects require a creature to attack different players or planeswalkers, such as that of this scheme and that of Gideon Jura’s first ability, that creature’s controller chooses one to fulfill.