"Legacy of the Duelist" is very ideal, as "Sphere Mode" would only be summoned by "Immortal Phoenix" in the End Phase, and "Legacy" allows you to add a monster from the Graveyard during your turn, at the expense of giving up your normal draw, so you can constantly retrieve "Ra" and summon it when your turn begins and "Sphere Mode" is still on your side of the field, creating a small loop.
The effects of cards like "Foolish Burial" are extremely useful for enabling this card's Special Summon effect, as well as any card effects that are capable of sending this card from the hand to the Graveyard.
The last effect of "The Winged Dragon of Ra" can be used on itself to trigger this card's Special Summon effect.
Speaking of this deck, a good card that works well with this card, "Ra", and "Mound of the Bound Creator", is "Beelzeus of the Diabolic Dragons". "Beelzeus" can be summoned by using 2 Level 4 Monsters, and a Level 2 DARKSpellcasterTuner searchable by "Timestar Magician". 1 - "Beelzeus" can make you gain life points before or after using Ra's or this card's effects. 2 - Since "Beelzeus" is also Level 10, combining it with "Mound of the Bound Creator" can make it both untargetable and indestructible. 3 - Since this card is unaffected by other cards' effects, it can attack even though "Beelzeus" is on your field.