No.
As long as the monster is in Defense position, White Ninja will destroy the target monster. So if Medusa worm was flipped face-down again by its effect, then yes, but if it is still in attack position, then no.
there is only 1 sphinx and it is located in ancient Egypt
No. It is specifically stated on the card lore that it "cannot be Special Summoned except by paying 500 Life Points when both "Andro Sphinx" and "Sphinx Teleia" are destroyed at the same time..."
No, it is not considered a Summon. Therefore, the effects of cards such as Golem Sentry are not activated as it requires the card to be FLIP SUMMONED. However, it is considered to be "flipped" meaning that Flip Effect Monsters' effects are activated when successfully attacked.
Magic planter
You cannot manually. Such an occurence could only result from a card effect.
Best place to watch any episodes of Yugioh, Yugioh GX, Yugioh 5D's, and Yugioh Zexal is at the website 4kidstv.com
None of those cards are really worth much.
Series after: yugioh 5'ds is yugioh Zexal.
Go to Yugioh-cards.com to check for updates when new tuornament on yugioh 5'ds be out.
He can't destroy them by battle, but he can destroy them with his effect. No, Copycat's effect targets, and Obelisk can't be targetted.
It becomes an Equip Card when it resolves, and as such, will remain on the field until it loses its target - like if the equipped monster is flipped face-down or leaves the field.
Walmart or a yugioh store.