zacian-c is fixed to donate base zacian stats, as the crowned variant is a forme change at the beginning of battle.
anyway I'm bored of zacian-c teams, here's my rain build without one:
it's not close to perfect but it'll cheese most matchups and get by others with some good plays. you probably autolose to a non braindead Ferrothorn core tho.
HP slot: Rotom-H serves as the catch-all pivot, taking hits from stuff like Zacian and Marowak-A and pivoting out to the rain sweepers. Zekrom gives it nice chunky HP so it won't die. Trick is absolutely vital to disabling a key wall like Eternatus, Shuckle, or Quagsire, and it's generally fine to click it immediately so you can do wall stuff later. Third slot is optional because you really only click Trick and Volt Switch, so Rain Dance/Defog/Toxic/Thunder Wave are legit options. I've been liking Thunder Wave for parahax - especially clutch when a wall or tank can't heal at the right time against your watery onslaught.
ATK slot: Seismitoad kills stuff off Zekrom's 150 attack. EQ two hits Pex on the switch, Power Whip one hits Quag and two hits most bulky waters, and Liquidation handles everything else under rain. PuP helps the Pex matchup even more, preventing it from spamming Recover, which makes me like the physical variant a lot more than the special one. LO can be Lefties, I think you kill walls all the same, but prepare to miss some kills on some offensive threats.
DEF slot: Excadrill is a decent suicide lead, it gets up rocks, spins webs away, and sacs with Steel Beam. Can be SDef slot honestly, but the Def makes it easier to deal with Pikachu if you save it for trades midgame. Speaking of trades, saving your sash for endgame is a good way to eliminate pesky Eternatus or Marowak when the chips are down and weather is gone.
SPA slot: Mantine is the most consistent Hydro Pump spammer here, since STAB Specs Hurricane is not a bad move to be locked into (unlike Kingdra or Ludicolo's coverage options). Being Ground-immune is also clutch against Sticky Web and TSpikes, which would otherwise severely sap your momentum. Click Surf or Hurricane 90% of the time, saving Hydro Pump for things like Zacian-C or when you really want to get that 40% chip on a grass-type. Fourth slot is optional: emergency Defog clears the field for your other sweepers when the fan's shat, and Roost is nice if you choose to run LO.
SDEF slot: Pelipper goes here, though it could easily trade spots with Excadrill. Generic set, nothing much to say. I don't like Defog or Roost as this team plays too fast. Weather Ball/Surf over Scald is acceptable, or Hydro Pump if you're feeling frisky.
SPE slot: Zekrom, the ace in the hole. This baby sets up on too many things. Rillaboom? Bait. Toxapex? Bait. Quagsire? 2HKO with +1 Outrage thanks to Unaware. Bolt Strike at +1 is a 75% roll to OHKO Zacian-C, which is nice when it hits. Fucked by Ferro and Tangrowth so you better chip them hard with your swift swimmers. Dragon Claw also works over Outrage if you're wary about being played around, but the power will be sorely missed at times. Same goes for Fusion Bolt over Bolt Strike.
Also this team has a Pikachu problem so just press X (or run Lefties + Protect on Seismitoad, or force it to 1v1 one of Exca/Zekrom, or somehow Trick it with Rotom).
edit: for extra fun, Excadrill can be replaced with a Clefable @ Damp Rock carrying SR/Moonblast/Healing Wish, and either Rain Dance or Softboiled. Healing Wish is great against teams that rely on stalling for LO recoil or poison to whittle the rain sweepers down. A second Rain Dance lets you set up rain more aggressively with Pelipper, and save Rotom-H to make trades later in the game. If you're running this variant, Mantine can be LO instead of Specs so you can click Defog more reliably.
edit2: other, friskier options over Mantine include Drednaw, which notably resists Pikachu's FO/ESpeed, and can potentially forgo specs with Power Herb Meteor Beam.