Demon of Death's Gate

• WWizards of the Coast2010-08-15
  Official Ruling
  Casting Demon of Death's Gate by paying its alternative cost doesn't change its mana cost or mana value.
• WWizards of the Coast2010-08-15
  Official Ruling
  Casting Demon of Death's Gate by paying its alternative cost doesn't change when you can cast it. You can cast it only at the normal time you could cast a creature spell.
• WWizards of the Coast2010-08-15
  Official Ruling
  Effects that increase or reduce the cost to cast Demon of Death's Gate will apply to it even if you choose to pay its alternative cost.

Rulings via Scryfall