Target player activates a mana ability of each land they control. Then that player loses all unspent mana and you add the mana lost this way.
10/4/2004 This card forces the target player to draw mana from lands if they are untapped, but that player can choose how to draw the mana if a land they control has multiple mana abilities, or mana abilities with choices.
10/4/2004 Your opponent may use instants and abilities of permanents in response to this spell before you get the mana from their mana pool and lands.
10/4/2004 If a land can draw a variable amount of mana, the target player (not the player of this spell) chooses how much to draw.
4/15/2013 A mana ability is an ability that (1) isn’t a loyalty ability, (2) doesn’t target, and (3) could put mana into a player’s mana pool when it resolves.