Text (LG+errata): {4},{Tap}: For one spell this turn, you may spend mana as though it were mana of any color to pay that spell's mana cost. (Additional costs are still paid normally.) [Oracle 2007/02/01]
Cannot be used to power the X portion of Drain Life with any color mana because the draining portion of Drain Life has the mana usage limited in the text. [D'Angelo 1999/07/26]
Effects like Planar Gate and Mana Matrix can end up paying for all the spell's mana cost. [Aahz 1994/09/02]
Extended tournaments (see Rule 913) have always banned this card.
