Mystic Restraints

Flash
Enchant creature
When Mystic Restraints enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Boomerang

Return target permanent to its owner's hand.

Ronin Warclub

Equipped creature gets +2/+1.
Whenever a creature you control enters, attach Ronin Warclub to that creature.
Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)

Higure, the Still Wind

Ninjutsu {2}{U}{U} ({2}{U}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Higure, the Still Wind deals combat damage to a player, you may search your library for a Ninja card, reveal it, put it into your hand, then shuffle.
{2}: Target Ninja creature can't be blocked this turn.

Slither Blade

Ornithopter

Keiga, the Tide Star

Flying
When Keiga, the Tide Star dies, gain control of target creature.

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Mistblade Shinobi

Ninjutsu {U} ({U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Mistblade Shinobi deals combat damage to a player, you may return target creature that player controls to its owner's hand.

Ninja of the Deep Hours

Ninjutsu {1}{U} ({1}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Ninja of the Deep Hours deals combat damage to a player, you may draw a card.