CardName: Conservation of Ninjutsu
Cost: 1b
Type: Enchantment
Pow/Tgh: /
Rules Text: Whenever a nontoken creature you control attacks and isn't
blocked, you may pay {1} and return that creature to your
hand. If you do, put two 2/1 black Rat Ninja tokens onto the
battlefield tapped and attacking the player or planeswalker
of your choice.
Flavour Text:
Set/Rarity: Multiverse Design Challenge Rare
Conservation of Ninjutsu
R
Enchantment
Whenever a nontoken creature you control attacks and isn't blocked, you may pay and return that creature to your hand. If you do, put two 2/1 black Rat Ninja tokens onto the battlefield tapped and attacking the player or planeswalker of your choice.
See Rat Ninja and Challenge # 145.
Forgot crucial clause: "and isn't blocked"