Seed Guardian

• WWizards of the Coast2016-01-22
  Official Ruling
  Use the number of creature cards in your graveyard as the ability resolves to determine the value of X. Seed Guardian will count toward this number as long as it’s still in your graveyard at that time.
• WWizards of the Coast2016-01-22
  Official Ruling
  Once the Elemental is created, the number of creature cards in your graveyard changing won’t cause the Elemental’s power or toughness to change.

Rulings via Scryfall