This was the MVP in the team I used to top the Doubles Ubers ladder.
Gen 8 Doubles Ubers
Zamazenta-Crowned @ Rusted Shield
Ability: Dauntless Shield
EVs: 252 HP / 112 Atk / 108 SpD / 36 Spe
- Wide Guard
- Behemoth Bash
With it's kit of support moves, Zamazenta-C is definitely a top 2 support Pokémon in Doubles Ubers. Wide Guard completely blocks all spread moves, including but not limited to Calyrex-S's Astral Barrage, Groudon's Precipice Blades and Kyogre's Water Spout, allowing your ally to attack or set up more safely (if you successfully block a spread move) and sometimes making the opponent Dynamax their spread attacker. Unlike Protect, Wide Guard can be used consecutively and not fail, meaning it can actually be spammed (although a good player will probably have stopped using spread moves by that point). Behemoth Bash is Zamazenta's main attacking move. Coaching gives your ally a Bulk Up boost (+1 attack, +1 defense), increasing both their power and bulk on the physical side and potentially allowing them to snowball through teams. Coaching also goes through Protect and ignores redirection, so Zamazenta can give it's ally stat boosts without fear of them getting knocked out before they can attack, or an opponent stealing the boosts. Snarl lowers both of the opposing Pokémon's special attack, allowing Zamazenta's team to take special hits better.
252 HP EVs and 108 Special Defense EVs allow Zamazenta to always survive a Max Geyser from Kyogre in Rain (coming off of Water Spout) from full health, in case they Dynamax when you attempt to block a Water Spout with Wide Guard. 36 Speed EVs and a Jolly Nature allow Zamazenta to outspeed max speed Xerneas and Yveltal, as well as a +1 16 Spe Groudon. The rest of the EVs are in attack so Zamazenta isn't as passive (although this does enable a 2HKO on Calyrex-S and 3HKO on Zacian-C, both with Behemoth Bash)
Zamazenta-C is an amazing team mate for Ho-Oh. With Coaching support, Ho-Oh is capable of completely destroying teams thanks to the attack boost and can have it's Weakness Policy activated more safely with it's improved physical defense (even allowing it to take a Max Rockfall from Groudon if Ho-Oh is Dynamaxed). It also appreciates Wide Guard support, blocking Kyogre's spread moves, allowing it to set Tailwind more safely or dent opponents with powerful max moves. Ho-Oh also obliterates Zacian-C, which is capable of easily 2HKOing Zamazenta-C.