Suicune's mono-water typing and wonderful stat distribution will always allow it a place in OU, however, its viability will be severely hampered without access to Scald if it doesn't get that move. Without the ability to threaten physical attackers with a burn on the switch-in, a lot of Suicune's potential utility is shattered. Would likely run a Calm Mind Scald Rest Talk set (unless it gets some new, even more viable options).
Sacred Fire - could potentially be a solid offensive utility attacker with Sacred Fire, Extreme Speed, Crunch, and Tera Blast (
leaning towards Tera Blast Ground at the moment) as it's not required to run Choice Band like Harcanine is.
This is going to be Raikou's best generation offensively since GSC/ADV imo - Calm Mind with Tera and the myriad of its coverage options is fantastic (
recall that last gen it had access to Aura Sphere, Extrasensory, Scald, Shadow Ball, and Weather Ball - if it gets even a few of those alongside Tera Blast, it'll have a solid OU niche).
Latios still hits hard and is decently fast, but being a Pokemon weak to Dark, Ghost, Bug, Ice, and Fairy in this current meta is going to hurt its viability quite a bit (
although Tera will alleviate that somewhat). Levitate, great coverage and solid offensive stats are working for it.
I think this will be the first generation where Latias is going to be the consistently better choice compared to Latios - Tera Steel/Poison defensive variants with Levitate sound nasty with its access to reliable recovery; it's a great lure for Pokemon like Iron Valiant and I'm looking forward to using it in OU.
Steel/Fighting is a great type combination, and 108 Speed is a pretty usable but frustrating benchmark (
although Jolly 252 Cobalion does outspeed Enamorus, Adamant Cinderace, Modest Greninja, Adamant Ogres and all the base 100s, which is nice). Plus, Cobalion has a nice base 129 defense stat in addition to the ability Justified (
helping it in its potential role as a check to non-Low Kick Kingambit variants). It could have a neat niche in OU as a Taunting Stealth Rocker with momentum via Volt Switch and the ability to check Kingambit. (
+2 252+ Atk Supreme Overlord 5 allies fainted Kingambit Sucker Punch vs. 0 HP / 0 Def Cobalion: 156-183 (48.2 - 56.6%) -- 89.1% chance to 2HKO).
As much as I love Virizion, it's got extremely strong competition this gen; Breloom is a much better utility Grass/Fight Pokemon overall, while Lilligant-H is a much better offensive Grass/Fighting type overall. Chesnaught is very solid and Decidueye-Hisui has a small niche. If they give Virizion access to additional utility moves (
Leech Seed, Stealth Rock, etc), I could see it being a specially bulky SubSeed user with the ability to check Kingambit, but otherwise, its potential for a place in OU is very shaky.
Most likely the most solid of the trio - Rock/Fighting is a phenomenal offensive typing in the current meta, with its STAB combination nailing OU Pokemon like Blissey, Ceruledge, Cinderace, Dragonite, Enamorus, Garganacl, Greninja, Heatran, Iron Moth, Kingambit, Rock-Oger, Ribombee, Hamurott, Skeledirge, Ting-Lu, and Zapdos super effectively (that's a huge portion of OU right there).
Baxcalibur on steroids. Kyurem-B is likely not staying in OU if it drops.
While it has less attack than Baxcalibur (
Baxcalibur has 145 attack while Kyurem has 130 attack and Kyurem is additionally rumored to have lost access to Roost) and lacks the Thermal Exchange ability, Kyurem's bulk (
125/90/90) is far better than Baxcalibur's (
115/92/86) and Kyurem can additionally run mixed sets thanks to its base 130 Special Attack stat as well. On top of that, Kyurem's base 95 Speed stat is critical compared to Baxcalibur's 87 speed stat which allows Kyurem to outpace both Great Tusk and Landorus-Therian (
Baxcalibur has a speed tie with Tusk and is outsped by Landorus-T). Regardless of whether Kyurem loses both Roost and Earth Power, I don't see him staying in OU.
If it drops to OU for testing in DLC 2, I can see it being strong but not overwhelming. Darkrai usually needs a setup turn regardless of the main sets it would likely be running, and choice items are situational at best. Additionally, being limited to Focus Blast/Tera Blast for fighting coverage is pretty disappointing. The tier is already in a state of hyper-dark-type awareness due to Kingambit, Greninja, Ting-Lu, and Hamott so some potential checks and counters are well documented. Along with those previously mentioned woes, Darkrai feels very pressured Tera-wise (
both against threats it could potentially take down and what Tera-type to use itself). Overall, I think it would be a solid addition to the OU meta (
likely A- to A rank imo).
Depending on Flygon's utility movepool, it could have a small niche as a technical utility Pokemon (
especially if it retains access to Defog and U-Turn). Its stat spread is looking pretty meager by OU standards these days though. Hopefully it will get some buffs, but otherwise, it's looking like Flygon will likely not see much OU play.
Potentially a really fun Sticky Webs setter - Compound Eyes with STAB Thunder along with STAB Bug Buzz and access to coverage like Giga Drain is solid. Its 108 Speed tier is frustrating (although outpacing Manaphy and potentially threatening an OHKO is nice), and its bulk/defensive typing are paltry, but then again, so are Ribombee's. If Galvantula gets access to Sleep Powder, it will definitely have a niche as an OU webs setter.
Reuniclus is a great mon overall with multiple fantastic abilities, access to reliable recovery, and Tera to alleviate its problems with Dark-type and Ghost-type threats. I can see both Magic Guard and Regenerator variants becoming solid niche choices in OU.
I have to agree with
awyp that Necrozma is extremely slept on and is only going to get better with the advent of Tera + likely some small additional movepool options. Great setup moves, a fantastic ability, a wide offensive movepool, and solid stats all across the board, I can see Necrozma being placed UU but being a frequent niche mon used in OU.