Invasion of Arcavios // Invocation of the Founders
Copy engines that persist on the battlefield have always been among the most feared permanents, because they compound instead of resolving: each spell you cast pays out twice, and nothing about that resets when the turn ends. The back half doubles every instant or sorcery cast from your hand, so burn deals twice, card draw draws twice, a removal spell answers two threats, a ritual pays for itself and then some. Reaching it is the whole cost. The enters trigger on the Siege tutors an instant or sorcery from your library, your graveyard, or outside the game, which means the front side exists to guarantee you arrive at the flip already holding a spell worth doubling. Then the Siege mechanic hands protection to a chosen opponent, and the controller becomes the aggressor: you have to muster damage against a defended battle to break its defense counters before the game moves on, and only then do you exile it and cast the enchantment for free. The two faces are one idea split across a transform: find the payoff, then make it happen twice. The defense timer sets the terms for everything that follows, asking the controller to commit a board capable of cracking the Siege quickly, and to punch through whatever the protecting opponent throws in the way, before the promised copy engine ever lands.
