Here is how the Eternal Earth Source will be found in Rise of the Portal Masters.
A while later they arrived at the ruins with the hot air balloon in a wrecked state, Mickey placed the Crystal Eye on the Core of Light.
Mickey Mouse: There, it's done.
Li’l Cheese: We did it!
Twilight Sparkle: Good work, all of you.
Luster Dawn: Thank you, Princess Twilight.
Master Eon: Well done, you have brought back the Crystal Eye.
Soon, the Core of Light was gaining more power than ever before.
SpongeBob SquarePants: Isn't this incredible, Dijon?
Dijon: It sure is, SpongeBob. Dijon has never seen anything like it.
Squidward Tentacles: Oh joy.
Georgia: Get a grip, Squidward.
Hugo: Thank you. Now, we must get the Eternal Earth Source. The Villagers in Stonetown have recovered it and are keeping it safe until we arrive.
Flynn: Whoo-Hoo! Yeah! Finally, an easy one! What did I tell ya!? Cake!
Hugo: Sure. Except for Kaos, the growing Darkness and the foul-smelling Cyclopses, all looking for the very thing that we are after.
Flynn: Oh, yeah. Well, heh. I guess if you count those...
Hugo: I'm sure Diggs knows the way, we should ask him.
So, they went to see Diggs.
Diggs: Say, how's about a visit to Stonetown?
SpongeBob SquarePants: Are you ready for this, Launchpad?
Launchpad McQuack: Ready when you are, SpongeBud.
So, they packed their belongings for their next assignment.
Soon, they finally came to Stonetown.
Thomas the Tank Engine: We made it to Stonetown.
Diggs: Alright, this is as far as I can take you guys. Stonetown is just beyond this Cyclops outpost, but the ground is shaking something terrible. All these vibrations... I sense something is very wrong here!
Meanwhile not too far at Stonetown, the civilians were all crying for help.
Civilian: Help! It's the Eternal Earth Source! It's become a hideous, horrific, terrible monster!
Back with SpongeBob, Launchpad, and the others, they begin their rescue at once.
SpongeBob SquarePants: Looks like it's all up to us, Launchpad.
Launchpad McQuack: No time to lose! Let's go!
Just as they got through Stonetown, they came to the Stone Golem.
Stone Golem: (roars)
SpongeBob SquarePants: Nice monster. Nice monster. Not a nice monster!
Just as the Launchpad saved SpongeBob, the Skylanders fought off the Stone Golem.
Spyro: Stealth Elf, let's take him down.
Stealth Elf: Right behind you, Spyro.
At last, they were about to finish off the Stone Golem.
Spyro: Terrafin! Bash! Now!
Terrafin: That's our cue!
Bash: Here we go!
At last, they finally took down the Stone Golem as the Eternal Earth Source appeared.
Rocker: The Stone Golem is down and out!
At last, the Eternal Earth Source was absorbed inside the Earth Ring.