2004-10-04 : If a land can draw a variable amount of mana, the target player (not the player of this spell) chooses how much to draw.

2004-10-04 : 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.

2004-10-04 : 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.

2013-04-15 : 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.