The Ninja are old and have children trained by a master named Khanji (Don't confuse). Their allies are also old. Their children's names are Selena, Austin, Owen, Will and Mark.
At the Bounty
Lloyd: Ninja, I think it's time to retire and continue as masters. Let our children do the job. Khanji. Train them old friend.
Khanji: As you wish my friend.
The Ninja leave
Khanji: Students. You are the ninja team from now. Your parents are too old for the job.
New ninjas: Got it!
Far away a portal opens and a dark figure steps out
Dark Figure: Finaly I am back to Ninjago! Fear me peapole as I the Master of Shadows had risen again!
At the Bounty
Austin: Master are you ok?
Khanji: I feel darkness. Evil. Destruction. Shadow. And no light or any good.
Austin: Could it be your evil brother you told us about? Lord Dragondon?
Khanji: He was banished from Ninjago long ago. But there is a bigger evil I have not warned you about yet.
Mark: Who is it?
Khanji: The Master of Shadows. He is an ancent figure of evil, and when he returns, what is most likely happened right now, then a great darkness will come. Worse than the Great Devourer, worse than the Overlord, worse than the Preeminent. And only the combined power of all elements can stop it.
Selena: We are four. He is alone.
Khanji: Sadly he is not alone. He has an army of shadows. And I can see some dark things.
Owen: Like what?
Khanji: I can see the soul of a broken hero.
Khanji: I don't know. But I can also see the end of my brother's long banishment.
In the Dark Island
Lord Dragondon: I was banished here for a long time. Until now. Now I am finaly free and can concuer Ninjago! Hahahahahaha!
Dragondon uses his powers to teleport back to Ninjago only to meet up with the Master of Shadows
Dragondon: Who are you
MOS: I am the Master of Shadows!
Dragondon: Why are you here?
MOS: I want to cause fear in the citizens of Ninjago, and to bow before me.
Dragondon: I think we can make a perfect team
MOS: Yes. With our powers combined we can cause darkness and destruction in Ninjago!
MOS: Shadows! You have a new commander Lord Dragondon! He will help us complete our goals.