Ninja element is not used often in Little Alchemy 2, but it can be used to combine Ninja Turtle. Making Ninja is a complicated process, you have to make Star, Life, Human, Metal, and Shuriken first. We have figured out the easiest way for you. Check out the detailed instructions and try it yourself.
Earth + Earth = Land
Earth + Land = Continent
Continent + Continent = Planet
Fire + Planet = Sun
Air + Planet = Atmosphere
Sun + Atmosphere = Sky
Time + Sun = Day
Time + Day = Night
Sky + Night = Star
Fire + Earth = Lava
Lava + Earth = Volcano
Water + Water = Puddle
Water + Puddle = Pond
Water + Pond = Lake
Lake + Lake = Sea
Earth + Sea = Primordial Soup
Volcano + Primordial Soup = Life
Earth + Water = Mud
Air + Air = Pressure
Earth + Pressure = Stone
Air + Stone = Sand
Sand + Mud = Clay
Clay + Life = Human
Human + Stone = Tool
Tool + Stone = Hammer
Hammer + Earth = Ore
Ore + Fire = Metal
Star + Metal = Shuriken
Shuriken + Human = Ninja