Ultra Beasts

An Ultra Beast (Japanese: ウルトラビースト Urutora bīsuto) is a type of creature introduced in Generation VII and was revealed on September 6, 2016.

Description
In the Alola region, rumors are flying about mysterious creatures known as Ultra Beasts. Ultra Beasts possess mighty powers and could pose a threat to humans and Pokémon, so they are feared. It appears that the Aether Foundation is also conducting research on these Ultra Beasts.

Just today 4 uncatchable pokemon ultrabeasts were added ct-50, ct-51 sensei, ct-51 invert. As it is rumored that these ultra beasts are or maybe legendary Pokémon

Known Ultra Beasts
Apparently, multiple Ultra Beasts exist, each of them called by a code name.

UB-01/Nihilego
UB-01 (Japanese: UB01) is the first Ultra Beast shown. It was revealed on September 6, 2016.

UB-01’s body is composed of a glass-like substance. However, it’s constantly changing shapes, never settling on one.

While evidence of something like a survival instinct can be observed in UB-01, no one knows whether it has a will of its own or any emotions. It’s said that, for some reason, its movements resemble those of a young girl.

UB-02
UB-02 (Japanese: UB02) is the second Ultra Beast shown. It was revealed on September 12, 2016 through the September issue of CoroCoro magazine.

UB-02 comes in two different variations, depending on the game version. Pokemon Sun comes with UB-02 Absorption, while Pokemon Moon comes with UB-02 Beauty. According to the scan, both of them would be encountered facing off Tapu Koko in their respective games.

UB-02 Absorption/Buzzwole
This is the Ultra Beast set to appear in Pokémon Sun.

The extent of its strength is unknown. Its entire body is covered with bulging, powerful muscles. The full force of a punch powered by these muscles would be off the charts! Its distinctively long mouth is said to be harder than diamonds. Could the Ultra Beast also use it to attack?

UB-02 Beauty/Pheromosa
This is the Ultra Beast set to appear in Pokémon Moon.

Its narrow, graceful legs allow it to accelerate with such explosive speed that people claim it can dodge lightning! It is said that any Pokémon that sees UB-02 Beauty, regardless of its own gender, will become infatuated with it and lose the will to battle. The exact reason for this reaction—whether it's an unidentified pheromone exuded by UB-02 Beauty or a hypnotic effect induced by its appearance—has not been determined. It is also unknown if it affects Genderless Pokémon.