Rayquaza

As you go through certain Ultra Wormholes while traveling through Ultra Space, you will sometimes land in an area where, as you land, you are told there is a strong presence coming from the area - this is a clue that a Legendary Pokemon is there. All Wormhole Legendary Pokemon can be found in there Shiny Forms, and after catching all the Legendary Pokemon of a specific location in the Ultra Space Wilds, you will be notified that the presence there is now gone.

By traveling through a Red Ultra Wormhole, you sometimes will be able to find and thus battle the Legendary Pokemon Rayquaza. However, you will only have the chance of finding it if you have both Kyogre and Groudon in your party. Rayquaza is a Dragon / Flying Type Pokemon, and it will be found at Level 60 knowing the moves of Rest, Extreme Speed, Dragon Pulse, and Dragon Dance.