The way Catrina and Princess Luna to the rescue goes in The Night to Remember.
Twilight Sparkle: Is it really you?
Star Swirl the Bearded: Yes, Princess Twilight Sparkle. I've heard you've been quite a fan.
Spike: How'd you know all that?
Star Swirl the Bearded: I know everything, Spike. But I didn't come alone.
Plankton: Can he be wise or what?
Then, Scorpan appears and is happy to see Princess Celestia again.
Scorpan: Hello Princess Celestia, It's been so long.
Princess Celestia: It sure has, Scorpan. You haven't changed a bit.
Scorpan: But still the same friend.
Discord: Fancy seeing you here, Scorpan.
Star Swirl the Bearded: So, You're here as well, Discord?
Scorpan: Shouldn't you be causing chaos in Equestria?
Discord: Not anymore, You see, I've been completely reformed by Fluttershy and I've learned that Friendship is Magic, Then your so called "brother," Tirek tricked me into believing that he could offer me something more then Friendship, But I now realized that there is nothing worth more.
Scorpan: So, Tirek betrayed you too? That's the one thing you and I had in common. He did it to me twice. Come, we must continue our quest.
As our heroes made it through the trench.
Thomas: We've made it.
Nellie: (reading the billboard) Gargoyle Canyon. Dead ahead.
Joy: Let's go save Princess Luna!
Aranea: for Equestria!
Catrina: Finally, Right where I want you!
Dusty Crophopper: Uh oh.
Luke: Who are you?
Catrina: Name's Catrina, I'm here to kill you
Wreck-It Ralph: Kill us?
SpongeBob SquarePants: Listen, miss, can't we talk about this? We don't want any trouble.
Catrina: I was being hired by Aku.
Catrina: Yes, he wanted me to exterminate you.
Patrick Star: Exterminate us?
Catrina: That's right.
Sunil Nevla: She is one bad Feline!
Vinnie Terrio: Those are big claws!
Catrina: Don't worry. This'll only hurt a lot! (evilly laughs) I love this job!
Then, Princess Luna came to the rescue.
Princess Luna: Hold it right there, Catrina!
Princess Celestia: Luna!
Hiro: Luna! (hugs his bride-to-be) How did you escape?
Princess Luna: I had a little help.
Jiminy Cricket: (chuckles)
Maleficent: Well, Isn't that brave of you, Jiminy.
Wreck-It Ralph: YOU!
Maleficent: Calm yourself, Wreck-It Ralph. I'm not here to fight, I've come to warn you all.
Sandy Cheeks: What in tarnation do ya want ta' warn us about, Maleficent?
Maleficent: I've overheard Aku trying to kill you along with Twilight and the others, Catrina!
Catrina: What? That's impossible! How could this happen?
(During Flashbacks after Catrina sets off)
Maleficent: Do you really put your trust in Catrina, Aku?
Aku: Of course I don't, Maleficent. This is all part of my plan to have Samuria Jack destroyed along with Princess Celestia and her foolish freinds.
Starlight Glimmer: You're as bad as I was, Aku. It's just us ruling the world!
Maleficent: (to herself) Except for Catrina. (vanishs without a trace)
(The flashbacks ends)
Maleficent: And that's why I've come to aid you all.
Stephen: We're glad you're on our side.
Shining Armor: Thanks for warning us, Maleficent. For once, we owe you one.
Grumpy: Let's get out of here!
Plankton: Before it's too late!
Gobo: Before Aku catches us.
Red: and Ruin the Wedding.
Zoe Trent: I wonder how'll we ever get back home.
Then, They heard an evil laugh.
SpongeBob SquarePants: Who was that?
Samurai Jack: Aku!
Aku: Well done, Maleficent. We have them right where we want them, Finish the job.
Maleficent: Never, Catrina will be destroyed as well.
Aku: Do as I say!
Maleficent: I won't, Catrina is my friend. We are not pawn of your wicked game!
Aku: Oh? But you are and If you won't obay, then I'll make you. (laughs and begins to control Maleficent)
Maleficent: Luna, Look out. I can't stop him! (blasts)
Princess Luna: Everyone, Watch out! (dodges)
Catrina: Stop this, Maleficent!
Maleficent: I can't, Aku is using us as puppets!
Aku: (laughs and begins to control Catrina)
Maleficent: Out of the way! (blasts)
Sunset Shimmer: No!
Then Sunset was hit and is badly hurt.
Twilight Sparkle: Sunset!
Scorpan: She's still alive.
Star Swirl the Bearded: But bearly, Come, We must find shelter while we still can.
Samurai Jack: I understand, it is not your fault, Maleficent. It is all Aku's doing.
Catrina: Aku, We curse your name. We will no longer serve onto you, We will make you pay and Dearly!