PTE Redux Status: Questionable. Regardless of whether or not Amphibia will be introduced in PTE, Amphibia itself will be its own dimension, entirely separate from Mewni.
Role in the series
Anne ends up learning that Amphibia is a world with origins from The Bestiary Dimension, the original home of the monsters of Mewni, who were initially destroyed by a Xexaxez and then resurrected by a Resurrectorate, given another chance and formed seeds that created Amphibia through the monster race known as the Batarchiogs, or amphibian people, far unrelated to the monster race of Buff Frog, that were one of the far more tender-hearted monsters of the Bestiary Dimension. But the toad breed that spawned the toad warriors were the original breed and thusly they were the closest to monsters.