It's right there.

Masterful Ninja's first activated ability doesn't cause any enters-the-battlefield abilities to trigger. When the turn ends and Masterful Ninja stops being both on the battlefield and in your hand, this won't cause any dies or leaves-the-battlefield abilities to trigger. If Masterful Ninja enters or leaves the battlefield some other way, those abilities work as normal.

Look closer.

If you try to move Masterful Ninja from the battlefield to your hand or vice versa, and it's in both zones, it will just stay in both zones. For example, if Masterful Ninja is in both zones, casting Unsummon targeting it won't do anything.

No, that's a table.

If Masterful Ninja is destroyed or discarded, it goes to your graveyard. It will no longer be on the battlefield or in your hand.