Fallen Shinobi

Any cards you don't cast will remain in exile.

The creature with ninjutsu enters the battlefield attacking the same player or planeswalker that the returned creature was attacking. This is a rule specific to ninjutsu; in other cases, when a creature is put onto the battlefield attacking, that creature's controller chooses which player or planeswalker it's attacking.

As you activate a ninjutsu ability, you reveal the Ninja card in your hand and return the attacking creature. The Ninja isn't put onto the battlefield until the ability resolves. If it leaves your hand before then, it won't enter the battlefield at all.

Although the Ninja is attacking, it was never declared as an attacking creature (for purposes of abilities that trigger whenever a creature attacks, for example).

Fallen Shinobi's triggered ability doesn't change when you can play the exiled cards. For example, if a sorcery card is exiled, you can cast it only during your main phase when the stack is empty. If a land card is exiled, you can play it only during your main phase and only if you have an available land play remaining.