Pokémon Center Plush are plush released by the Pokémon Center that are typically not associated with any other plush lines (such as the Pokédoll range) or any Pokémon Center Collections. They are standard plush - made out of minky with more detailed parts being made of other materials, and they are usually anywhere from 8" (21cm) to 14" (38cm), though some will of course be a little shy of this range either way. There are also mascot sized plush and lifesize plush available in this range.
Typically, these plush are released in waves of 3-6 (though sometimes more or less dependsing on different collections or games releasing on the same day), and they are usually released according to the current generation and games. As well, it is worth noting that all starter forms and the box legendaries consistently receive these plush in each generation, and many of the Pokémon that are revealed during the lead up to a new generation are highly likely to receive these plush as well.