Here is how the Skylanders returned in Rise of the Portal Masters.
Later, Twilight, SpongeBob, Mickey, Thomas, Mumfie and their friends brought Glacier, Rocker, Heater, Wild Flower, Topper, Geary, Skuller and Tide to meet Yen Sid.
Mickey Mouse: Master Yen Sid, We've brought eight visitors that might interest you.
Yen Sid: Bring them in.
When the chosen Portal Masters came to see Yen Sid, He was amazed that they had the Rings of the Skylanders.
Yen Sid: Can this be true, After all these years? You have found the chosen Portal Masters.
Twilight Sparkle: Yes.
Then, Mickey and Mumfie brought all the Skylanders who're frozen in figure statue forms.
Mumfie: We've just found them as well as all the Portal Masters are together again.
Mickey Mouse: Is there a way to reawaken them, Master?
Yen Sid: Only the chosen Portal Masters of any elements can reawaken the Skylanders.
Just as the Portal Masters gathered together, They freed the Skylanders are returning from their frozen figure forms with a few glows of their Rings.
Spyro: Where are we?
Gill Grunt: We are in some sort of castle.
Trigger Happy: Guys, It's the Portal Masters with their Rings!
Cynder: That means we're free from being frozen like statues.
Yen Sid: Without the Skylanders, Skylands will be in great danger because of Kaos.
Launchpad McQuack: What kind of Chaos, Master Yen Sid?
Scrooge McDuck: No, Launchpad. He means Kaos, K-A-O-S!
Mickey Mouse: What can we do, Master Yen Sid?
Yen Sid: Hmmm... It would seem that it'll be entirely up to you all, the Portal Masters and the Skylanders. You must go to Skylands and stop Kaos from ruling it.
Mumfie: We'll do our best, Yen Sid.
SpongeBob SquarePants: I know we will.
Eruptor: Then, What're we waiting for?
Slam Bam: Let's go kick some butts!
Yen Sid: Go, And good luck to you all.
So, They left to save Skylands and Equestria.