When the screenshots of what Solgaleo and Lunala look like when becoming one with Necrozma, many fans thoughts these would be new Forms for the original Cover Legends of the 7th Generation. However, these forms actually belong to Necrozma after it somehow absorbs the two legends separately. When becoming one with Solgaleo, this is called Necrozma's Dusk Mane Form; when with Lunala, this is called its Dawn Wings Form.
It has now been revealed that when Necrozma changes to these new Forms, its typing will remain that of the Cover Legend it is absorbing. In its Dusk Mane Form, Necrozma will become a Psychic / Steel Type Pokemon (like Solgaleo originally is); in its Dawn Wings Form, Necrozma becomes a Psychic / Ghost Type Pokemon (like Lunala is by itself). Some fans were expecting new typings to be given to these new forms of Necrozma; however, since Necrozma is a pure Psychic Type on its own and Solgaleo and Lunala are both part Psychic, it only made sense that it would gain the Dual Typing of the Legend it is absorbing. When in its two new forms, Necrozma will also continue to have the Prism Armor Ability.