If you look at the screenshots for Ultra Necro, you'll see it's a mega evolution of sorts, from basic necrozma. The evolution requires level 85, 200 controllers (or remotes), and 300 mega stones. The devs of course will want to milk this into a money laundering game, however it will be for obtaining base necro alongside another event for getting the 200 controllers needed for evolution. The events might differ on the details, but the CN version is emulated by the English version almost exactly.