Gravity Field

Does Gravity Field's cost depend on who performs the move or who controls the moved unit?Copy Anchor Link

The player performing the move must pay 1 if they are an opponent of Gravity Field's controller, regardless of who controls the moved unit.

The player who performs a game action is responsible for it.^[412.1] Charm and Siren's Song each instruct you to move an enemy unit, so you perform the move even though your opponent controls that unit. If an opponent controls Gravity Field at the destination, you must pay the cost; if you control it there, neither player pays.^{[204.4][204.4.a]} By contrast, Call to Battle instructs the chosen opponent to move one of their units, so that opponent must pay the cost if you control Gravity Field at the destination.

Must an opponent pay Gravity Field's cost when an effect tells them to move a unit to its battlefield, or can they decline?Copy Anchor Link

They must pay 1 to perform the move, but they may decline. If they decline or cannot pay, they move no unit.

For example, Angler Wyrm and Call to Battle each instruct a chosen opponent to perform the move, so that opponent is responsible for it.^[412.1] Gravity Field therefore applies its cost to that move action.^{[204.4][204.4.a]} Applied costs are paid as their associated game actions are performed.^[204.4.b]

The word "must" does not remove the option to decline an applied cost. If the opponent declines or cannot pay, they cannot perform the move action.^[204.4.c] The move instruction is negated rather than ignored because it cannot be followed for a reason other than an illegal target or unavailable information.^{[359.3.e.6][407.5]}