Necrozma Dusk Mane is a great partner with zygarde.
Necrozma-Dusk-Mane @ Rocky Helmet
Ability: Prism Armor
EVs: 216 HP / 252 Def / 40 Spe
- Sunsteel Strike
- Thunder Wave
- Morning Sun
- Stealth Rock
Necrozma takes care of one of the biggest threats in the meta, Zacian. It easily chips zacian and can eventually take it out with sunsteel strike or helm chip, while also outspeed it when it (zacian) is paralyzed with the 40 speed evs. This is good because zacian can hard counter zygarde after zygarde takes a good bit of chip damage. While scaring out zacian, it can set up rocks without much worry, giving you free chip and them needing to get a defogger out. With thunder wave, necrozma spreads paralysis through the opponents team, giving zygarde a free chance to set up or even just crippling the opposing team. Zygarde and Necrozma is such a good defensive backbone, and almost no physical attackers can get past it. Sorry for the sloppy explanation, idk what to say since ndm is pretty straightforward.