Oswald Fiddlebender

• WWizards of the Coast2021-07-23
  Official Ruling
  An artifact's mana value is determined solely by the mana symbols printed in its upper right corner (unless that artifact 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 that's also an artifact, for example), its mana value is 0. Ignore any alternative costs or additional costs (such as kicker) paid when the artifact spell was cast.
• WWizards of the Coast2021-07-23
  Official Ruling
  A token has a mana value of 0 unless it's copying something else.
• WWizards of the Coast2021-07-23
  Official Ruling
  If an artifact is copying something else, its mana value is the mana value of whatever it's copying.

Rulings via Scryfall