Unlimited format has no official tournaments, so it doesn't get much attention from Pokémon. However, the general statement that no cards are banned is correct, though with some caveats as below.
Jumbo cards are banned in tournaments per a ruling in the Compendium:
No, you cannot. You may only use cards that have been released for TCG play in the standard size. Jumbo cards are artistic representations of the legal card's art.
___'s Pikachu is legal to play in the Unlimited format.
Ancient Mew would be illegal due to the different card back.