Somberwald Sage

• WWizards of the Coast2012-05-01
  Official Ruling
  Mana produced by Somberwald Sage can't be spent on noncreature spells that would put creature tokens onto the battlefield.
• WWizards of the Coast2012-05-01
  Official Ruling
  Mana produced by Somberwald Sage can be spent on any part of a creature spell's total cost. This includes additional costs (such as kicker) and alternative costs (such as evoke costs).
• WWizards of the Coast2012-05-01
  Official Ruling
  Mana produced by Somberwald Sage can't be spent on activated abilities, even ones that put a creature card directly onto the battlefield, such as unearth or ninjutsu.

Rulings via Scryfall