Necrozma-Ultra A ---> A+
Necrozma-U, with a Dusk Mane base, reaps the benefits of both a defensive typing with matching stats before using the Ultra Burst and a more offensive typing with stats.

Necrozma-Dusk-Mane @ Ultranecrozium Z
Ability: Prism Armor
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Photon Geyser
- Swords Dance
- Earthquake
- Sunsteel Strike

Before Ultra Burst, Necrozma provides a reliable switch-in with its more defensive typing and stats. This makes it able to counter Xerneas and some Arceus formes even before Ultra Burst. After Ultra Burst, however, Necrozma has a drastic increase in its Speed and has a typing shift. With Swords Dance, it is able to reliably counter Groudon, Necrozma-DM, and most Arceus forms. It only has a few major checks, being Yveltal, Mega Gengar, and Marshadow (which isn't completely reliable with Shadow Sneak not OHKOing on most sets); however, these are checked with many common higher tier Pokemon.

After Swords Dance (which can be used quite easily in DM forme), Necrozma has sweeping ability comparable to (or even exceeding) Pokemon of the A+ tier, like Xerneas and Marshadow. It also far exceeds Pokemon of its tier, having far fewer checks than most of the Pokemon in A. Ultimately, due to its dual purpose as both a more defensive Pokemon with a matching typing and a more offensive Pokemon with matching speed stats and typing, Necrozma-Ultra is an incredibly powerful threat that is far more comparable to the Pokemon of A+ than the Pokemon of A.