From the reporters of the E3 there have been people who already played Sun/Moon Tree House demo and they confirmed at least two new Pokémon to appear in them.

>A lemon like Pokémon that reminds of Pineco and Ferroseed. Type: Plant/Electric
>A floating tribal mask Pokémon with a new attack called Conjuring. Type: Ghost

The names aren't known yet but probably will be revelaled in a few hours.