Smother

• WWizards of the Coast2010-03-01
  Official Ruling
  If a creature is copying something else, its mana value is the mana value of whatever it's copying.
• WWizards of the Coast2010-03-01
  Official Ruling
  A token has a mana value of 0, unless it is copying something else.
• WWizards of the Coast2010-03-01
  Official Ruling
  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 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.

Rulings via Scryfall