Offensive Mons that check Zamazenta Crowned in OU (no point in putting defensive ones, since there are too many, the style that Zamazenta can break is offense, not balance or Stall).
Skeledirge: As already posted yesterday, 252 HP, 0 Defense Skeledirge takes this:
252 Atk Zamazenta-Crowned Crunch vs. 248 HP / 0 Def Chandelure: 180-214 (43.7 - 52%) -- 11.7% chance to 2HKO < Other moves are resisisted even better.
Volcarona: This is 0 investment one:
252 Atk Zamazenta-Crowned Wild Charge vs. 0 HP / 4 Def Volcarona: 131-155 (42.1 - 49.8%) -- guaranteed 3HKO < Zamazenta can,t even attack reliable, since Flame Body is a thing. Bulkier Volcarona versions are even better, the moth lost Roost, but not Morning Sun.
Zapdos:
252 Atk Zamazenta-Crowned Ice Fang vs. 0 HP / 4 Def Zapdos: 154-182 (47.9 - 56.6%) -- 85.5% chance to 2HKO < This is the only move Zamazenta has for it. It does 2HKO, but comes at the price of not having both STABs, Crunch, Wild Charge or Howl. Static is also a thing and Zapdos learns Heat Wave.
Sun in general. Torkoal is not an offensive Mon, but supports many of them that obviously smash Zamazenta with Fire moves. Torkoal itself easily switches into Zamazenta to do whatever it wants.
Goldengo:
252 Atk Zamazenta-Crowned Crunch vs. 252 HP / 0 Def Aegislash-Both: 172-204 (45.5 - 53.9%) -- 2% chance to 2HKO after Leftovers recovery < I expect Max HP Goldengo + Recover to be common in offensive teams. Crunch is the only move Zamazenta can use vs him, rest are walled. Zamazenta can use Howl to break through Goldengo, but that comes at the price of not having Wild Charge or Ice Fang for other Mons.
Great Tusk:
252 Atk Zamazenta-Crowned Close Combat vs. 0 HP / 0 Def Donphan: 147-174 (39.6 - 46.9%) -- guaranteed 3HKO < 0 investment Great Tusk can switch at least once.
Iron Hands:
252 Atk Zamazenta-Crowned Close Combat vs. 0 HP / 0 Def Hariyama: 174-205 (38.7 - 45.6%) -- guaranteed 3HKO < Can switch at least once with 0 investment. This Mon is slow, so it won,t invest in speed, meaning that it will have some investment in either HP or Defense.
These are just offensive (Stall and Balance get way more options) Mons that switch into Zamazenta and can check it. Zamazenta is supposed to be a Mon that switches into offensive threats and checks them with high offensive power, bulk and speed, however its very hard for him to actually do that, since the meta is extremely offensive and Hazard centered, which are extremely hard to remove (and Zamazenta Crowned can,t run Boots).
My opinion is that not only Zamazenta Crowned doesn,t break the Meta, similar cases can be said about Zamazenta Hero and Giratina-A, though this is all theorymoning, since the we are not getting neither of these Mons before Home and by then Meta can change a lot (and some Moves added).