Here is how Tigatron and Airazor arrived and Stewie tells his story goes in Yuna, Stewie and Brian.
Princess Cornelia: Tigatron, Airazor, Thank you both for coming on such short notice.
Tigatron: We're just glad to come, Princess Cornelia.
Airazor: Especially for Yuna.
Moon Starlight: Yuna is trapped somewhere in the mine.
Prince Isamu, Prince Indy and Princess Anna: (crying)
Princess Celestia: There, There. Little one, We'll find Yuna.
Princess Sharon: Hugo, Rita, You two are with us to go find Yuna, Brian and Stewie.
Rita the Fox: No problem, Sharon.
Princess Luna: First, We must wait for Tigatron and Airazor to let us know if they've seen her.
Tigatron: (goes into Beast Mode) We're ready.
Airazor: (goes into Beast Mode) And we won't stop until they're found.
Princess Celestia: Very good. Go, And good luck.
So, Tigatron and Airazor set off to find Yuna, Brian and Stewie.
Prince Isamu: (crying)
Prince Indy and Princess Anna: (crying)
Princess Celestia: Sharon and I will take care of Indy and Anna.
Moon Starlight: There, There, Isamu. It's alright. (brought out her old baby toys) Here, These are my old toys.
Prince Isamu: (feels much better)
Princess Luna: Have fun playing with them.
Princess Sharon: Where are you, Yuna?
In the caverns.
Princess Yuna: (waiting) What is taking so long!?
Stewie Griffin: If it'll make you feel better, Princess. I'll tell you the whole story about how I saved Brian from death before Vinny.
Brian Griffin: I've never remembered Stewie saving my life.
Princess Yuna: Please tell us!!
Stewie Griffin: All right.
Brian Griffin: I hope it'll all come back.
In the flashback.
Stewie Griffin: (time travels and sees Brian) Brian, Look Out! (saved Brian from a runaway car)
Brian Griffin: WHAT THE HECK!?
Stewie Griffin: You're Alive, My Friend!
Brian Griffin: What? Of course I'm alive. What the heck is going on here?
The flashback ends.
Princess Yuna: Wow!
Stewie Griffin: And that's the whole story.
Brian Griffin: That was messed up.
Princess Yuna: It happens.
Stewie Griffin: Let's hope help will be on it's way.
Brian Griffin: And pray for a miracle.