Shinjitsu, Master of Patience

Each Ninja creature card that you own that isn't
on the battlefield has Ninjutsu. The Ninjutsu cost is equal to its mana cost.
Whenever a Ninja you control deals combat damage to a player, you may pay life equal to its converted mana cost. If you do, return that creature to your hand.
"There is a difference between falling back and retreating."