Drain Power

A mana ability is an ability that (1) isn't a loyalty ability, (2) doesn't target, and (3) could add mana when it resolves.

Your opponent may use instants and abilities of permanents in response to this spell before you get the mana.

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.