2010-03-01 : A creature's mana value is determined solely by the mana symbols printed in its upper right corner (unless that creature is copying something else; see below). If its mana cost includes {X}, X is considered to be 0. If it has no mana symbols in its upper right corner (because it's an animated land, for example), its mana value is 0. Ignore any alternative costs or additional costs (such as kicker) paid when the creature was cast.

2010-03-01 : A token has a mana value of 0, unless it is copying something else.

2010-03-01 : If a creature is copying something else, its mana value is the mana value of whatever it's copying.