Pokemon
Additions
Just BST-wise the strongest (legal) new face is Dragapult and its 600 BST. However, 142 of that is Speed. Nothing else really pushes the magic 625 cap so I expect the op teams to be similar, but there's some viable choices.
Rillaboom: Technically not totally outclassed for a Grass type thanks to its HP and Attack, but its special stats are lacking.
Cinderace: Entei is pretty much better, except with 1 less attack and slower.
Inteleon: Very poor defenses.
Greedent: It's fat. Feel like Snorlax or Type Null wins out.
Coalossoal: Probably better than Magcargo... Probably Worse than Mega Camerupt
Appletun: More defensive than Exeggutor-Alola?
Cramorant: Has an ability to itself and that's pretty much it. Imagine starting off with one of these ready to paralyze on hit.
Centiskorch: More balanced Volcarona? Rocks for days.
Hatterne: It's ok outside of HP, and it's nice and slow. Psychic/Fairy, could compete with Gardevoir. Actually the typing itself isn't really that defensive so it's not really important to compare with the same type.
Grimmsnarl: Unique typing. Unfortunately it can't rely on STAB in Metronomes. Usable stats
Cursola: Slow powerful ghost. This thing would appreciate hitting first.
Sirfetch'd: Because it can hold the Stick/Leek in the wild I hope it can wield it to full effect but the item description says otherwise. Much bulkier than Farfetch'd... The power
Mr. Rime: Lol ice type. I don't feel much towards it, though I don't have any experience using ice types to compare to so I guess it could pull off a weakness policy. It has stats Actually Mega Glalie is probably better.
Pincurchin: It's slow at least, slowest Electric type. Decent other than HP but the slow Electric role is occupied.
Stonjourner: Why imbalance doesn't work. Metronome tests all aspects not just one half of your stats.
Eiscue: The penguin I was looking forward to. Sadly its noish form gets better speed for lower defenses and it doesn't even have the good typing/stats of Mimikyu (assuming it works like Disguise). Meh unless Snow Warning is free.
Fossils: They look cool. 500+ bst is nice.
Dragapult: There's a CAP of this typing (Ghost/Dragon) that I've seen sometimes. It's a ghost + has stats so it'll definitely be a choice.
Eternatus Eternamax: Now that Blissey's gone, this can be the Impostor user of choice! Thank you gamefreak
Galarian Darmanitan: The strongest physical Ice type, dreaded snowman. It's cool
tl;dr Pokemon are stat blobs that have a typing that decides resistances and weaknesses. Think for yourself
Removals
Irrelevant since PS has everything.
Abilities
Additions
Intrepid Sword: Free +1 Attack (I assume). Like Download, but for physical attackers. Seems alright, you immediately get power so it's good for the short term.
Dauntless Shield: Same thing but for Defense. Harvest Kee Berry may be better boost wise, but again it's a good short term/immediate boost.
Gorilla Warfare: Apparently this is Choice Band, but as an ability. You can choose between this or +1 Sword, if you're concerned about your ability versus the volatility of stat stages, though I haven't done the math so it might work out either way. Assuming Choice + Metronome mechanics are the same, you also lose out on multi turn moves which can be pretty helpful. If you're making the sacrifice you can run Choice Specs/Band at that point for even offensive boosts or a 2.25x Attack boost.
EDIT: This is actually better than Hustle Band, as Ivy pointed out with the new Heracross strats.
Wandering Spirit: Could be fun. This will probably reactivate abilities like Intimidate or Download like Skill Swap does. A simple strategy is to run Protective Pads so you steal abilities and keep them for yourself. Kind of like Mummy then, but with less spreaders.
Perish Body: I feel like this will be banned. This ability seems very lame and would lead to very short games. Unlike Cursed Body it has to be a contact move, but the description makes it seem like it's a 100% perish. It kills the user but you have a chance to activate it again within the time you have to live. Plus you can just put this on two slow Pokemon, and force outslowing to be a win condition.
Neutralizing Gas: Abilities are neutralized as long as you live. This sounds okay in general, its actual utility will have to be tested.
Ripen: The concept sounds interesting, though Harvest strats may be better for most berry uses
Sand Spit: If Sand Stream is banned, then this will be banned. If you can take a hit you create sand.
Punk Rock: Ups offense and defense with Sound moves. Unfortunately the only important one is a status move.
Power Spot: Vague effect, but I'm predicting an offensive Friend Guard. Hopefully better than battery
Mimicry: This may be the one way you can actually control changing your type, the usefulness seems limited. No steel terrain
Ignore draw-in effects: Mold Breaker seems better. Moves still get drawn in, but it'll probably draw into something with a weakness and you ignore a lot of other abilities like Magic Bounce.
Libero: From what we know it's Protean. I don't agree with the initial ban but I'll point it out.
Gulp Missile: Pretty sure this will be Cramorant exclusive. Actually activating its form change will seldom happen, but it's based on formes so hopefully you can start with a gulp form and be able to paralyze on the first hit or something. The damage probably won't be too high.
Steam Engine: No immunity, speed bad.
Ice Scales: I don't know how good it will be but judging from Fluffy and Fur Coat it won't get a chance.
Steely Spirit: At best it could make your ally steel moves ohko everything. At worst it might make steel beam go from 90% to 100%.
Pastel Veil: Poison isn't much
Hunger Switch: I dont think this matters if you dont even have the move
Ball fetch: Another illuminate clone. Thank you game freak
tl;dr I don't think anything is on Magic Bounce's level/will be the new meta, but Perish Body sounds op
Removals
None. I guess they could get away with removing moves since they're in changeable slots and you can 'keep' them while being useless, but abilities always exist.
Moves
Additions
Clangorous Soul is an omniboost that costs HP. Nice
Decorate is a +2 to offenses on a target. If it's your teammate that's great, if the opponent then it's funny.
2x damage on Dynamax moves: I'm pretty sure these will be Metronome callable but not 100% confident. Will have good power in general, but Dynamax itself does not seem worth using. More on that later
Life Dew: Not that great but if it's callable I think this may be the only teammate healing move you can get.
Octolock: Now this is something. Lowering defenses every turn, very consistent.
Snipe Shot: I guess this can avoid a Storm Drain, if it actually has its effect when called via Metronome unlike the Alola legend sigs.
No Retreat: A 1 use omniboost. Very nice
Magic Powder: Another type changing move. Psychic isn't much compared to Grass and Ghost though, those are very defensive/weak.
Spirit Break: Another Fairy move to hit Sableye super effectively. Free pokestar spirit
Body Press: Looks usable with all the defense in this metagame.
Overdrive/Breaking Swipe: Spread moves. Always nice
Dragon Darts: It sounds cool
Eternabeam: If Prismatic Laser was callable, this might be callable. At the same time I doubt it, they always hide some legendary move.
Teatime: 90% of the time it's useless, 9% of the time it foils an Imposter+Leppa strat, 1% of the time it fuels an actual Berry strategy.
EDITS: Stuff Cheeks is another move that consumes your berry. I can't tell if it will give you the effect of the berry when you 'eat' it via the move because that sounds pretty good but if you're using a berry then it's usually easy to activate.
SNAP TRAP is another binding/free 50% damage move to replace Clamp. And it has 100% accuracy
Removals
Relevant because Metronome calls moves in the game. Let's Go, Z-moves, and past uncallable moves are irrelevant for comparing with the current [Gen 7] Metronome Battle. The loss of Return, Frustration, and Hidden Power is a mighty blow - no longer do we have to care about happiness values and setting a Hidden Power type in the teambuilder. In general some of these moves were kind of weak, which might make Weakness Policy 'riskier'. Rolling Ice Ball was basically a win if you could survive and hit the full 5 turns, especially with it being Ice so that'll be missed. Foresight and Odor Sleuth means that Ghosts are slightly better. Natural Gift will let berries be more consistent I guess. I'm mixed about Bide, on one hand it could be a big hit and on the other hand you're open for 3 turns (though not using PP). Embargo also makes your item usage more consistent? Barrier is an actually 'good' move that's gone. So is Clamp, with its major passive damage.
All in all we didn't lose that much of the move pool, but we did lose some classics and niches and Metronome will be lesser as a result. Thank you gamefreak. I'll miss the occasional Silver Wind omniboost, bugged Synchronoise, Rototiller buff, or Ion Deluge play. There's probably some strong moves that I looked over because of not having secondary effects to mention. At this moment we're still waiting on move data for buffs/nerfs.
EDIT!!!!: There is a "CanUseMove" flag that may be implying that a ton of past gen sig moves are unusable but their descriptions weren't cut and caught. We may say goodbye to the useless duo of Dark Void and Lunar Dance, but this could mean major losses of high-damage moves. The actual mechanics of Metronome still have to be tested though. Also, Sunsteel Strike/Moongeist Beam/Nature's Madness may have been removed from the pool itself.
Items
Additions
Room Service: Better off using that CAP ability Persistent if you want something to happen with rooms
Throat Spray: Sound moves are not very useful to play around
Blunder Policy: It boosts speed when you miss.
Utility Umbrella: Not very clear on what "effects of weather" it protects from
Eject Pack: Useless
Rusted Sword: According to Zacian's dex entry, this is known as the "Fairy King's Sword". How much weight can you handle?
The new items are not very game changing for Metronome Battles. Thank you gamefreak
Dynamax/Gigantamax
Megas and Z-moves died for this. And what is it? Making you big/doubling your HP for 3 turns, but also turning Metronome into basically Protect and making you useless. And they run off the same PP counter too so you don't even save anything by doing it. Maybe it could help stall if you can use it after getting Taunted/when you're forced to Struggle but I doubt it. Gigantamax doesn't even make a bit of difference since it only affects offensive moves. At most you can put a big pikachu in your party and get to see a broken square sprite (remember Melmetal?). The most accessible mechanic, but also the most useless one. We don't actually know all about how it works, but it doesn't look like Metronome is getting any special treatment.
EDIT: Actually Max Guard does directly help with a strategy, the dumb shedninja strategy because it lets you live turn 1 and they will not give shedinja more than 1 hp. Damn
out with its signature Shields Down and see if Weakness Policy would work well with it. I found two of them to be frail, so I put a Type Null 
with Friend Guard + Eviolite as a partner. Unfortunately I lost some data including my saved highlights, but my recent replays all use that team. It's too bad you can't do something like have Minior get hit and pull out a Delta Stream midway to block it further. In the end it was kind of fun. Rock typing helped with resisting moves and sometimes the strategy actually worked with getting hit and changing forme. It's nice that Shields Down changes your form at the end of the turn, so if the opponent hits you twice it's with your full defenses up. Though if you're due to attack after getting a boost that turn, you still have to do it with Meteor form's attacking stats. At this point I think what I wanted was Stance Change.
