Hello! great game!! The Winged Dragon of Ra - Sphere Mode only can summoned in the opponent field.

lore: "Cannot be Special Summoned. Requires 3 Tributes from either side of the field to Normal Summon to that side of the field (cannot be Normal Set), then shift control to this card's owner during the End Phase of the next turn."
Sphere Mode works as it should. You can tribute summon it to your opponent's side of the field or your side of the field depending on which side the monsters tributed are.