* "Mammoth Graveyard" is a Field Spell card. Field Spells are not monsters and cannot be used in Fusion Summoning. They are placed on the field zone, not the monster zone.
* Fusion Summoning requires Monster Cards. Fusion Summoning involves combining specific monster cards to create a Fusion Monster. Field Spells are not eligible for this.
Therefore, you cannot use "Mammoth Graveyard" as a material for Fusion Summoning.